Snapshots erratic and unreliable, with errors in log
# Bug Report

### Describe the Bug
I've been using Homebridge-ring for a couple of years now, and it's a great plugin.

However, the snapshot performance has always been slow and unreliable, and seems to be getting worse.

I also use Homebridge-ffmpeg and Homebridge-nest-cam to handle various cameras. When opening the home app, they both provide snapshots pretty promptly in general, whereas Homebridge-ring often takes several minutes to produce one, and often fails completely.

Here are some recent logs associated with this:

```
[2/27/2021, 11:28:00 AM] [Ring] Snapshot for Side Door failed to refresh after 70 attempts.  This is normal behavior since this camera is unable to capture snapshots while streaming
[2/27/2021, 11:28:00 AM] [Ring] Failed to cache snapshot for Side Door (46.109s), The camera currently reports that it is online
[2/27/2021, 11:28:00 AM] [Ring] Failed to cache snapshot for Side Door (35.153s), The camera currently reports that it is online
[2/27/2021, 11:28:00 AM] [Ring] Failed to cache snapshot for Side Door (12.108s), The camera currently reports that it is online
[2/27/2021, 11:28:00 AM] [Ring] Failed to cache snapshot for Side Door (1.195s), The camera currently reports that it is online
[Side Door] Snapshot request handler provided empty image buffer!
[2/27/2021, 11:30:04 AM] [Ring] Snapshot for Side Door failed to refresh after 70 attempts.  This is normal behavior since this camera is unable to capture snapshots while streaming
[2/27/2021, 11:30:04 AM] [Ring] Failed to cache snapshot for Side Door (47.862s), The camera currently reports that it is online
[2/27/2021, 11:30:04 AM] [Ring] Failed to cache snapshot for Side Door (36.898s), The camera currently reports that it is online
[2/27/2021, 11:30:04 AM] [Ring] Failed to cache snapshot for Side Door (25.842s), The camera currently reports that it is online
[2/27/2021, 11:30:04 AM] [Ring] Failed to cache snapshot for Side Door (14.929s), The camera currently reports that it is online
[2/27/2021, 11:30:04 AM] [Ring] Failed to cache snapshot for Side Door (3.835s), The camera currently reports that it is online
[2/27/2021, 11:31:00 AM] [Ring] Snapshot for Side Door failed to refresh after 70 attempts.  This is normal behavior since this camera is unable to capture snapshots while streaming
[2/27/2021, 11:31:00 AM] [Ring] Failed to cache snapshot for Side Door (48.693s), The camera currently reports that it is online
[2/27/2021, 11:31:00 AM] [Ring] Failed to cache snapshot for Side Door (37.707s), The camera currently reports that it is online
[2/27/2021, 11:31:00 AM] [Ring] Failed to cache snapshot for Side Door (26.686s), The camera currently reports that it is online
[2/27/2021, 11:31:00 AM] [Ring] Failed to cache snapshot for Side Door (15.698s), The camera currently reports that it is online
[2/27/2021, 11:31:00 AM] [Ring] Failed to cache snapshot for Side Door (4.733s), The camera currently reports that it is online
[2/27/2021, 11:33:25 AM] [Ring] Snapshot for Side Door failed to refresh after 70 attempts.  This is normal behavior since this camera is unable to capture snapshots while streaming
[2/27/2021, 11:33:25 AM] [Ring] Failed to cache snapshot for Side Door (50.728s), The camera currently reports that it is online
[Side Door] Snapshot request handler provided empty image buffer!
[2/27/2021, 11:38:32 AM] [Ring] Snapshot for Side Door failed to refresh after 70 attempts.  This is normal behavior since this camera is unable to capture snapshots while streaming
[2/27/2021, 11:38:32 AM] [Ring] Failed to cache snapshot for Side Door (50.031s), The camera currently reports that it is online
```

Please note that this does NOT appear to be associated with the camera stream being online with another client and therefore inaccessible, despite what it says in the logs. 

The workaround for this issue is to open a live stream by tapping the camera in the Home app. The live stream always opens promptly, and when I close it again there is a snapshot, which then usually refreshes on time. So the camera is definitely accessible – it's just that the snapshot handler is failing for some reason.

### To Reproduce
Open Home app.
No snapshot appears for Ring camera for a long time, if ever.

### Expected behavior
A snapshot should appear within a few seconds of opening the Home app.

### Homebridge Ring Config
```

{
    "refreshToken": "eyJhbGciOiJIUzUxMiIsImprdSI6Ii9vYXV0aC9pbn...",
    "platform": "Ring"
} 

```

### Environment
 - OS: MacOS 11.2.2
 - Node.js: v14.15.5
 - NPM: v6.14.11
 - homebridge-ring: v9.15.3
 - homebridge: v1.3.1

NOTE: In all cases, the same behaviour was observed with many previous versions.
