*** Original commit ***
Rollback of https://github.com/google/ExoPlayer/commit/e60609e34447553474cdfc86b2dee5462316b10c
*** Original commit ***
Prevent creation of new sessions if the Timeline is empty.
We currently create sessions based on the placeholder window
index. This shouldn't be needed as we now set a non-empty
timeline as soon as the first MediaItem...
***
PiperOrigin-RevId: 369609523
