Fixes: out of array read
Fixes: 19129/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_V210_fuzzer-5068171023482880
Maybe fixes: 19130/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_V210_fuzzer-5637264407527424

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegReviewed-by: Limin Wang <lance.lmwang@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>