Add conditional chaining to prevent for each fail on undefined

https://github.com/maxinminax/node-mihome/blob/e60c287d9bb2d9ba9123543d92ec481be5a62b5e/lib/device-miio.js#L192

Changing the line to 
```javascript
properties?.forEach(property => {
```
 should prevent the script from failing if the attribute is undefined.
The issue occured using Smart Fan 2 as the attribute was not defined there