Regression since: af1761f7
Fixes: Division by 0
Fixes: ffmpeg_crash_1
Found-by: Thuan Pham, Marcel Böhme, Andrew Santosa and Alexandru Razvan Caciulescu with AFLSmart
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 16d8b13b3b26c19d7f8856e039fe6662d96b4ff3)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>