Fixes: signed integer overflow: 6500736 * 473 cannot be represented in type 'int'
Fixes: 23259/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MV30_fuzzer-5179394271477760

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 3b8d5bcc3189c6c46279889f1176c0caba4466e4)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>