When the furthest-behind stream is being fed by a demuxer that is also
feeding packets to a choked filter graph, we need to unchoke that filter
graph to prevent the demuxer from getting stuck trying to write packets to
the choked filter graph.
This situation can also apply recursively - if the demuxer is also writing
to a filtergraph that is also reading from a choked demuxer, there is a
similar deadlock.
Solve all such deadlocks by just brute-force recursively unchoking all
nodes that can somehow prevent this demuxer from writing packets. This
should normally not result in any change in behavior, unless audio/video
streams are badly desynchronized, in which case it may result in extra
memory usage from the too-far-ahead stream buffering packets inside the
muxer. (But this is, of course, preferable to a deadlock)
Fixes: https://code.ffmpeg.org/FFmpeg/FFmpeg/issues/20611
Backported-From: 133a0bcb13
5418fbb7f4