When exporting compositions with multiple images in a row, transformation could
get stuck if a shader was ready to accept input when end-of-stream was already
signaled and queued from upstream. Fix accounting for the downstream capacity.
Manually tested on concatenations with several images and several videos in a
row, by adding logging and verifying the capacity updates as expected across
edited media item transitions.
PiperOrigin-RevId: 532088793
(cherry picked from commit 73d05d5d9dc6fdf06c59c6cb2247efba3bbc9f86)
