Fixes: OOM
Fixes: 1906/clusterfuzz-testcase-minimized-4599315114754048

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 a1c0d1d9)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>