Fixes: runtime error: signed integer overflow: 2052929346 + 204817098 cannot be represented in type 'int'

This was missed in b1bef755
Fixes: 5275/clusterfuzz-testcase-minimized-5367635958038528

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 c837918f)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>