There is an additional failure path I didn't account for in my previous
work. While I ensured that a late hwdec failure in receive_frame can be
recovered from by trying the next hwdec, there is a specific
combination where if an hwdec fails in receive_frame, and the next
hwdec is a full decoder (eg: v4l2m2m), and that also fails, we are left
with no decoder and so the entire decoding process ends and playback is
stopped.
Basically, we must keep re-attempting the fallback in receive_frame
until we get a valid decoder (software or hardware). This edge case
will rarely be encountered as there are only a couple of decoder based
hwdecs.
Fixes#11947
Philip Langdale
fbd0be1cf4