avcodec/svq3: Fix memleaks upon allocation error
Commit
b2361cfb94738298a6c4037cc348fe5015efb841e made all of the
error paths in svq3_decode_init() call svq3_decode_end(); yet several
new error paths that were added later (in merges from Libav) returned
directly without cleaning up properly. This commit fixes the resulting
potential memleaks by setting the FF_CODEC_CAP_INIT_CLEANUP flag. This
also allows to simplify freeing by returning directly.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>