fix(ReactExoplayerView): return unset track index when there are no t…

[rrosatti]

…rack available

This fix was integrated on version 4.0.0. We need it in order to fix a problem
on Android, where the video freezes on the first frame when using a remote url
instead of an asset.

link to the upstream PR:
TheWidlarzGroup#1233

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[abnerf]

@rrosatti if this patch belongs to someone else and was already merged upstream, lets not recreate it here. Just cherry-pick the original commit into our repo. Would that work for you?

[rrosatti]

@abnerf it worked just fine! Sorry for that. I should have done it before!

I've just updated the PR, cherry picking the commit from master.

[abnerf]

@rrosatti cool! Ship it!