Fixes: runtime error: signed integer overflow: -2143827186 - 7404944 cannot be represented in type 'int'
Fixes: 4354/clusterfuzz-testcase-minimized-4671122764201984

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