Still images not updating


**Describe The Problem:**
Within the Home app, the snapshot does not update automatically. 

**To Reproduce:**
If you don't watch the live stream, only stay on the main screen, the still image will never update.

**Logs:**

```
[My Home/Garage Ext/5838ACC3-AFCE-59AA-B7FF-4174391329D6] Accessory sent Error Domain=HMErrorDomain Code=50 "Accessory sent an invalid response" UserInfo={NSLocalizedDescription=Accessory sent an invalid response} for snapshot request of resolution HMDVideoResolutionType1280x720
```

**Homebridge Config:**

```ffmpeg -i http://xxxx@xxxx/cgi-bin/snapshot.cgi?Channel=0 -t 1 -vf scale=1280:720 -f image2 -```

**Screenshots:**


**Environment:**
v3.0.1
