Fixes: 768/clusterfuzz-testcase-4807444305805312
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit a66c6e28b5)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>