[Tempest Weatherflow] When station offline: 1) history repeats last measurement forever, 2) one warning per minute in log
My Tempest Weatherflow local weather station has been down for a few weeks now. Root cause: dead battery due to gloomy Belgian winter skies, that are so densely gray you'd believe the sun has been replaced by a single shitty TL-light 🤣😭

The WiFi-connected base station is still live though, so this Homebridge plugin still continues to communicate with it just fine.

Two bugs occur:

1. the Eve "fakegato" history views continue to show the last measurement in perpetuity. Whereas in reality, they should report "no data".
2. a JS error occurs for the `RainBool` characteristic, despite no new data being available:
```
[12/6/2023, 2:22:11 AM] [homebridge-weather-plus] This plugin generated a warning from the characteristic 'Rain': characteristic value expected boolean and received undefined. See https://homebridge.io/w/JtMGR for more info.
[12/6/2023, 2:23:12 AM] [homebridge-weather-plus] This plugin generated a warning from the characteristic 'Rain': characteristic value expected boolean and received undefined. See https://homebridge.io/w/JtMGR for more info.
[12/6/2023, 2:24:12 AM] [homebridge-weather-plus] This plugin generated a warning from the characteristic 'Rain': characteristic value expected boolean and received undefined. See https://homebridge.io/w/JtMGR for more info.
[12/6/2023, 2:25:12 AM] [homebridge-weather-plus] This plugin generated a warning from the characteristic 'Rain': characteristic value expected boolean and received undefined. See https://homebridge.io/w/JtMGR for more info.
[12/6/2023, 2:26:12 AM] [homebridge-weather-plus] This plugin generated a warning from the characteristic 'Rain': characteristic value expected boolean and received undefined. See https://homebridge.io/w/JtMGR for more info.
```

Seems like a trivial edge case to fix 😊 

If I enable Homebridge's debug mode, I get this:

```
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Updating weather from Weatherflow Tempest
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Current Conditions for station 'Now': {
  AirPressure: 1009.2,
  Condition: 'Unknown',
  ConditionCategory: 0,
  Humidity: 87.9,
  ObservationStation: 'ST-00109058',
  ObservationTime: '04:35:52',
  Rain1h: 0,
  RainDay: 0,
  SolarRadiation: 0,
  Temperature: 11.41,
  TemperatureApparent: 11.260000000000048,
  TemperatureMin: 11.41,
  DewPoint: 9.480000000000018,
  UVIndex: 0,
  WindDirection: 'N',
  WindSpeed: 0,
  WindSpeedMax: 0,
  BatteryLevel: 0.5797101449275033,
  BatteryIsCharging: false,
  WindSpeedLull: 0,
  LightningStrikes: 0,
  LightningAvgDistance: 0,
  LightLevel: 0,
  TemperatureWetBulb: 10.091900266983295,
  SkySensorBatteryLevel: 100,
  SkySerialNumber: 'SK-',
  SkyFirmware: '1.0',
  AirSensorBatteryLevel: 100,
  AirSerialNumber: 'AR-',
  AirFirmware: '1.0',
  LightLevelSensorFail: 0,
  HumiditySensorFail: 0,
  TemperatureSensorFail: 0
}
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting AirPressure to 1009.2
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting ConditionCategory to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting Humidity to 87.9
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting ObservationStation to ST-00109058
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting ObservationTime to 04:35:52
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting Rain1h to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting RainBool to undefined
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] This plugin generated a warning from the characteristic 'Rain': characteristic value expected boolean and received undefined. See https://homebridge.io/w/JtMGR for more info.
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Error: 
    at CustomCharacteristic.RainBool.Characteristic.characteristicWarning (/usr/local/lib/node_modules/homebridge/node_modules/hap-nodejs/src/lib/Characteristic.ts:3011:105)
    at CustomCharacteristic.RainBool.Characteristic.validateUserInput (/usr/local/lib/node_modules/homebridge/node_modules/hap-nodejs/src/lib/Characteristic.ts:2887:12)
    at CustomCharacteristic.RainBool.Characteristic.setValue (/usr/local/lib/node_modules/homebridge/node_modules/hap-nodejs/src/lib/Characteristic.ts:2229:20)
    at TemperatureSensor.Service.setCharacteristic (/usr/local/lib/node_modules/homebridge/node_modules/hap-nodejs/src/lib/Service.ts:758:35)
    at WeatherPlusPlatform.saveCharacteristic (/usr/local/lib/node_modules/homebridge-weather-plus/index.js:473:24)
    at /usr/local/lib/node_modules/homebridge-weather-plus/index.js:273:15
    at Array.forEach (<anonymous>)
    at /usr/local/lib/node_modules/homebridge-weather-plus/index.js:271:39
    at Array.forEach (<anonymous>)
    at /usr/local/lib/node_modules/homebridge-weather-plus/index.js:258:27
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting RainDay to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting SolarRadiation to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting Temperature to 11.41
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting TemperatureMin to 11.41
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting UVIndex to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting WindDirection to N
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting WindSpeed to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting WindSpeedMax to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting WindSpeedLull to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting LightningStrikes to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting LightningAvgDistance to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting LightLevel to 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting BatteryLevel to 0.5797101449275033
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting BatteryIsCharging to false
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting DewPoint to 9.480000000000018
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting TemperatureApparent to 11.260000000000048
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Setting TemperatureWetBulb to 10.091900266983295
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Saving history entry
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] **Fakegato-timer: addData  Now {
  time: 1701937604.17,
  temp: 11.400000000000006,
  pressure: 1009,
  humidity: 88
}  immediate:  false
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting AirPressure: 1009.2
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting ConditionCategory: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting Humidity: 87.9
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting ObservationStation: ST-00109058
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting ObservationTime: 04:35:52
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting Rain1h: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting RainBool: undefined
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting RainDay: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting SolarRadiation: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting Temperature: 11.41
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting TemperatureMin: 11.41
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting UVIndex: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting WindDirection: N
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting WindSpeed: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting WindSpeedMax: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting WindSpeedLull: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting LightningStrikes: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting LightningAvgDistance: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting LightLevel: 0
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting BatteryLevel: 0.5797101449275033
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting BatteryIsCharging: false
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting DewPoint: 9.480000000000018
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting TemperatureApparent: 11.260000000000048
[12/7/2023, 9:26:44 AM] [homebridge-weather-plus] Persisting TemperatureWetBulb: 10.091900266983295
```

(Note that that `  ObservationTime: '04:35:52',` corresponds to the very last observation it received, a few weeks ago. So that is _sort of_ accurate.)