Fixes: negation of -2147483648 cannot be represented in type 'int32_t' (aka 'int');
Fixes: 6500/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DIRAC_fuzzer-4523620274536448

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