avdec_mpeg2video (and probably more): Huge memory leak in git master
This was introduced by !46 (merged)
Can be reproduced by running e.g. on http://samples.mplayerhq.hu/MPEG2/dothack2.mpg , which ends up using >500MB before the file is finished.
CC @tpm blocker for 1.16.2 as it was also backported