Fixes: "null pointer dereference" (actually misaligned access but the tools seem not to support this)
Fixes: 14551/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_V210_fuzzer-5088609952071680

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