Fixes: 4478/clusterfuzz-testcase-minimized-4752113767809024
Fixes: runtime error: signed integer overflow: -2147483626 + -319489 cannot be represented in type 'int'

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