after update to fritzos 7.20 temp did not work anymore 
**Describe the bug**
I have a 6590 with fritzos 7.12 and a dect200, all good.
But after update to fritzos 7.20 the plugin can´t read the temp anymore.
Switching is ok.

**Screenshots**
```
[8/19/2020, 8:39:46 PM] [FritzPlatform] [ERROR] DECT 200 Temperature: An error occured while polling state
TypeError: Cannot read property 'celsius' of undefined
    at SmarthomeAccessory.getStates (/homebridge/node_modules/homebridge-fritz-platform/src/accessories/smarthome.js:209:61)
```

**Desktop (please complete the following information):**

Node.js Version | v12.18.3
Npm Version | v6.14.6
homebridge Version 1.1.2


