Fixes: signed integer overflow: 40550400 * 128 cannot be represented in type 'int'
Fixes: 20331/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RV40_fuzzer-5676685725007872

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