Adjust initial selection of HlsChunckSource.InitializationTrackSelection

[matamegger]

With the changes done in 0670782, there exists the possibility that indexOf(group.getFormat(0)) returns -1 (i.e. the track is not part of the selection).
This will earlier or later result in an ArrayIndexOutOfBoundsException.*

After having a look at the BaseTrackSelection I assumed that the selectedIndex may not be -1 or in general any invalid index for the selection.
To always have a valid selection we just select the first one. (Which is basically equivalent to the previous behaviour if the above mentioned change was not implemented.)

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* I observed the exception in the updateSelectedTrack -> isBlacklisted call

[AquilesCanta]

I think the described behavior may happen when the master playlist's first stream-inf tag is an i-frame-only tag.

The fix looks good, but it introduces a (I assume involuntary) functional change: It will make preparation start with the lowest bitrate variant, which changes the historical ExoPlayer bevahior of choosing the first stream-inf in the master playlist. I think it could make sense to choose the lowest bitrate one, as a way to speed up preparation. But there are better ways of achieving this, so it's a change that should be analysed independently of this bugfix.

Thanks for reporting this. I will send a fix for this internally, since it's faster than us having a back and forth to get this merged.