It is only supposed to be freed by libavcodec for decoders, yet
avcodec_open2() always frees it on failure.
Furthermore, avcodec_close() doesn't free it for decoders.
Both of this has been changed.
Reviewed-by: James Almer <jamrial@gmail.com> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>