Fix stalls for demuxed content when reconnect after connection is broken

[OshinKaramian]

We have been seeing issues with streams starting back up after a disconnect.

To reproduce:

1. Load demuxed content, a sample can be found: https://bitdash-a.akamaihd.net/content/sintel/hls/playlist.m3u8
2. Allow the buffer to fill up.
3. Kill your internet connection
4. Allow the buffer to run out
5. Reconnect

Playback should continue, but instead it stays in a frozen state.

Description

Without this fix, if there are separate audio/video streams that are loaded, the player will download the video streams (not the audio streams) and playback will freeze.

I believe it is due to https://github.com/videojs/http-streaming/blob/master/src/media-groups.js#L189 since that will set the activePlaylistLoader to null here: https://github.com/videojs/http-streaming/blob/master/src/media-groups.js#L37 -> https://github.com/videojs/http-streaming/blob/master/src/master-playlist-controller.js#L484 -> https://github.com/videojs/http-streaming/blob/master/src/master-playlist-controller.js#L257. Thus the audioSegmentLoader is never restarted (and playback freezes).

There could be a better fix here, but I'm a little unclear what that might look like/how much work that would be (so any input there would be appreciated.

Specific Changes proposed

Restart the audioSegmentLoader if the tech is not in a paused state.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors