SDK / exoplayer

This situation happens if the first chunk to load is already behind the end
of the stream. In this case, the preparation never completes because
HlsSampleStreamWrapper gets stuck in a prepared=false and loadingFinished=true
state.

Gracefully handle this situation by attempting to load the last chunk if still
unprepared to ensure that track information is obtained as far as possible.
Otherwise, it wouldn't be possible to play anything even when seeking back.

Issue:#6314
PiperOrigin-RevId: 264599465