Fixes: signed integer overflow: -32768 * 196032 cannot be represented in type 'int'
Fixes: 15300/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FLIC_fuzzer-5733319519502336

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 54bd47f8)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>