Fixes: 13579/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG1_V4L2M2M_fuzzer-5753560726241280

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>