Even in this scenario, the frame still contains references to data that
won't be freed if the frame isn't unreferenced. And the AVFrame itself
will leak, too.

Fixes Coverity issue #1441422.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>