In function ff_mpeg_ref_picture(), it returns 0 on the error path that
the return value of av_buffer_ref() is NULL. 0 indicates success, which
seems to deviate from the fact. Set ret to AVERROR(ENOMEM) to propagate
the error status to the callers.
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>