Fixes: OOM
Fixes: 5733/clusterfuzz-testcase-minimized-4906757966004224

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 01370b31)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>