This passed all streams to mp_recorder_create(), even disabled ones. The
disabled streams never get packets, so recorder.c eventually errors out
with unrelated-looking errors. The reason is that recorder.c waits for
packets to appear on other streams, which in turn is because libavformat
refuses to mux empty streams anyway.
recorder.c could call demux_stream_is_selected(), which would have made
the patch much smaller. But this feels like a bad idea, since recorder.c
should use sh_stream only for metadata (and not in an "active" way), nor
should it care what demux.c is currently doing with it. So make the API
user (demux.c) pass only the streams it really wants.
Fixes: #6999
5a9046222b