Up until now the documentation of ff_bsf_get_packet_ref() allowed return
values >= 0 in case of success, whereas av_bsf_receive_packet() only
allows 0 on success. Given that for some bitstream filters the return
value of ff_bsf_get_packet_ref() is forwarded to the caller of
av_bsf_receive_packet() without any filtering, there would be a problem
if ff_bsf_get_packet_ref() actually returned values > 0. But it
currently doesn't and there is no reason why it should ever do so.
Therefore this commit aligns the return values of these functions by
restricting ff_bsf_get_packet_ref() to always returns 0 on success.
Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>