SDK / exoplayer

Follow-up to a comment on https://github.com/google/ExoPlayer/commit/6f0f7dd1be40c81cb056d82215ceabdd5a8a2a1a: Buffers that are useful to pass
to the sample/passthrough pipeline should either contain data or the
end of input flag. Otherwise, passing these buffers along is unnecessary
and may even cause the decoder to allocate a new input buffer which is
wasteful.

PiperOrigin-RevId: 411060709