Fixes: signed integer overflow: 1080285923 - -1130879337 cannot be represented in type 'int'
Fixes: 22002/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP9_fuzzer-6260237310099456

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