Fixes: signed integer overflow: -1625276744 + -1041893960 cannot be represented in type 'int'
Fixes: 5948/clusterfuzz-testcase-minimized-5791479856365568

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 33fe17bd)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>