Unable to read power consumption characteristics in Eve app
<!-- Provide a general summary in the Title above -->

### Expected Behavior
To be able to read power consumption characteristics in Eve app
<!-- If you're describing a bug, tell us what should happen -->
<!-- If you're suggesting a change/improvement, tell us how it should work -->

### Current Behavior
I'm trying to read power consumption Eve app but it does work. I get error logs, see below. 

<!-- If describing a bug, tell us what happens instead of the expected behavior -->
<!-- If suggesting a change/improvement, explain the difference from current behavior -->

### Steps to Reproduce (for bugs)
<!-- Please add a series of steps to reproduce the problem. -->

### Versions
<!-- Please run commands and include versions below. -->
- **Node**:       `14.15.0`
- **Homebridge**: `homebridge  v1.1.6`
- **Plugin**:       `v6.1.0`
- **OS**:    `Windows 10 Enterprise, 64-bit`     <!-- The version and architecture of your operating system -->

### Configuration
<!-- Please include the TplinkSmarthome platform section of your config.json file.
Paste between the the two ``` lines below.
-->
```json
 {
    "bridge": {
        "name": "Homebridge ECBD",
        "username": "**xxxxxxx**",
        "port": 51399,
        "pin": "**xxxxxxx**"
    },
    "accessories": [],
    "platforms": [
        {
            "name": "Config",
            "port": 8581,
            "platform": "config"
        },
        {
            "name": "TplinkSmarthome",
            "addCustomCharacteristics": true,
            "switchModels": [
                "HS110"
            ],
            "deviceTypes": [
                "plug",
                "bulb"
            ],
            "platform": "TplinkSmarthome"
        }
    ]
}
```

### Homebridge Log / Command Output
<!-- Paste relevant output between the two ``` lines below
  - Remove any sensitive information, passwords, etc.
  - If output is long:
    - Please extract only the relevant portions if possible (remove other plugin's output, etc)
    - Consider creating a gist, etc
  - However, please include the beginning of the log where the homebridge initialization happens if possible
-->
```
[11/11/2020, 10:03:03 PM] Loading 2 platforms...
[11/11/2020, 10:03:03 PM] [Config] Initializing config platform...
[11/11/2020, 10:03:03 PM] [Config] Running in Service Mode
[11/11/2020, 10:03:03 PM] [TplinkSmarthome] Initializing TplinkSmarthome platform...
[11/11/2020, 10:03:03 PM] [TplinkSmarthome] homebridge-tplink-smarthome v6.1.0, node v14.15.0, homebridge v1.1.6
[11/11/2020, 10:03:03 PM] [TplinkSmarthome] Configuring cached accessory: [Meter] undefined **xxxxxxxx**
Setup Payload:
X-HM://002474UDIKMEL
Enter this code with your HomeKit app on your iOS device to pair with Homebridge:             
[11/11/2020, 10:03:03 PM] Homebridge is running on port 51399.
[11/11/2020, 10:03:03 PM] [TplinkSmarthome] New Device Online: [Meter] plug [**XXXXXXX**] _IPIPIPIP_ 9999
[11/11/2020, 10:03:03 PM] [TplinkSmarthome] Adding: [Meter] plug [8006260480D50608FB88185031B8FB8D1D6C63C7]
[11/11/2020, 10:03:03 PM] [TplinkSmarthome] [Meter] Correcting Accessory Category from: OUTLET to: SWITCH
[11/11/2020, 10:10:26 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [0.17]: Unable to call updateCallback Amperes
[11/11/2020, 10:10:26 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [0.011]: Unable to call updateCallback KilowattHours
[11/11/2020, 10:10:26 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [39.84324000000001]: Unable to call updateCallback VoltAmperes
[11/11/2020, 10:10:26 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [234.372]: Unable to call updateCallback Volts
[11/11/2020, 10:10:26 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [17.946]: Unable to call updateCallback Watts
[11/11/2020, 10:10:36 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [0.182]: Unable to call updateCallback Amperes
[11/11/2020, 10:10:36 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [0.011]: Unable to call updateCallback KilowattHours
[11/11/2020, 10:10:36 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [42.656068]: Unable to call updateCallback VoltAmperes
[11/11/2020, 10:10:36 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [234.374]: Unable to call updateCallback Volts
[11/11/2020, 10:10:36 PM] [TplinkSmarthome] [Meter] fireCharacteristicUpdateCallback [19.543]: Unable to call updateCallback Watts'
```
