Fix multiple: runtime error: signed integer overflow: 6497 * 3409630 cannot be represented in type 'int'
Fixes: 2819/clusterfuzz-testcase-minimized-4743700301217792

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