Upgrade from 2.12 to 3.x with MQTT generates error in myQMqtt.subscribe
**Describe The Problem:**
Upgraded the plugin from `2.12` to `3.2` with MQTT configured; after restarting the Homebridge service, an exception is raised when the plugin subscribes to the topic.

Error message is: `TypeError: Cannot read properties of undefined (reading 'serial_number')`
with the top of the callstack being: `at myQMqtt.subscribe (file:///homebridge/node_modules/homebridge-myq/src/myq-mqtt.ts:165:60)`

**To Reproduce:**
Perform an upgrade from `2.12` to `3.x` (reproduced with `3.0`, `3.1` and `3.2`)

**Logs:**
```
[8/22/2023, 7:52:37 AM] [myQ] myQ API: Successfully connected to the myQ API.
[8/22/2023, 7:52:38 AM] [myQ] myQ API: Discovered device family garagedoor: Garage Door [Liftmaster WiFi GDO DC w/Battery Backup] (serial number: XXXXXXXXXXXX, gateway: XXXXXXXXXXXX).
[8/22/2023, 7:52:38 AM] [myQ] myQ API: Discovered device family gateway: My Home (serial number: XXXXXXXXXXXX).
[8/22/2023, 7:52:38 AM] [myQ] Garage Door: Enabling automation switch.
[8/22/2023, 7:52:38 AM] TypeError: Cannot read properties of undefined (reading 'serial_number')
    at myQMqtt.subscribe (file:///homebridge/node_modules/homebridge-myq/src/myq-mqtt.ts:165:60)
    at myQGarageDoor.configureMqtt (file:///homebridge/node_modules/homebridge-myq/src/myq-garagedoor.ts:302:25)
    at myQGarageDoor.configureDevice (file:///homebridge/node_modules/homebridge-myq/src/myq-garagedoor.ts:38:10)
    at new myQAccessory (file:///homebridge/node_modules/homebridge-myq/src/myq-device.ts:63:10)
    at new myQGarageDoor (file:///homebridge/node_modules/homebridge-myq/src/myq-garagedoor.ts:9:7)
    at myQPlatform.discoverAndSyncAccessories (file:///homebridge/node_modules/homebridge-myq/src/myq-platform.ts:248:56)
    at myQPlatform.updateAccessories (file:///homebridge/node_modules/homebridge-myq/src/myq-platform.ts:299:10)
    at processTicksAndRejections (node:internal/process/task_queues:95:5)
    at file:///homebridge/node_modules/homebridge-myq/src/myq-platform.ts:333:14
```

**Homebridge Configuration:**

```json
{
    "email": "myq-username",
    "password": "myq-password",
    "name": "myQ",
    "options": [
        "Disable.Opener.BatteryInfo",
        "Enable.Device.SyncNames",
        "Enable.Opener.Switch"
    ],
    "mqttTopic": "homebridge/myq",
    "mqttUrl": "mqtt-on-local-network",
    "platform": "myQ"
}
```

**Screenshots:**
<!-- If applicable, add screenshots to help explain your problem. -->

**Environment:**

* **Homebridge Version:** v1.6.1
* **Node Version:** v18.16.0
* **Homebridge-myQ Plugin Version:** 3.x
* **Apple Device and iOS / macOS / iPadOS / tvOS Version:** n/a
* **Operating System and OS Version:** Docker
