Hls adaptive streaming not working for audio only

### Issue description
Hls adaptive streaming not working with our Audio tracks (Hls file doesn't contain Video track)
We tested Exoplayer demo app, just replaced Hls source by our link.
Player always selects default stream with BANDWIDTH=140800, and never switches to BANDWIDTH=281600, tested on wifi connection.

### Reproduction steps
Just replace HlsSource link in demo app:
` case C.TYPE_HLS:
return new HlsMediaSource.Factory(dataSourceFactory)
// .setPlaylistParserFactory(
// new DefaultHlsPlaylistParserFactory(getOfflineStreamKeys(uri)))
.createMediaSource(Uri.parse("our hls url here"));
`

### Link to test content
Link will be provided by email

### Version of ExoPlayer being used
Exoplayer 2.9.3, branch release-v2

### Device(s) and version(s) of Android being used
Google Pixel, Android 9.0

### A full bug report captured from the device
Bug report will be provided by email