SDK / exoplayer

We check the fraction of the available duration we have already
buffered for live streams to see if we can increase the quality.
This fraction compares against the overall available media duration
at the time of the track selection, which by definition can't include
one of the availabe chunks (as this is the one we want to load next).

That means, for example, that for a reasonable live offset of 3 segments
we can at most reach a fraction of 0.66, which is less than our default
threshold of 0.75, meaning we can never switch up.

By subtracting one chunk duration from the available duration, we make
this comparison fair again and allow all live streams (regardless of
live offset) to reach up to 100% buffered data (which is above our
default value of 75%), so that they can increase the quality.

Issue: google/ExoPlayer#9784
PiperOrigin-RevId: 416791033