Fixes: index 32 out of bounds for type 'uint32_t [32]'
Fixes: 63003/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-4685160840560640

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