avcodec/4xm: Fix signed integer overflows in idct()
Fixes: signed integer overflow: 20242 * 121095 cannot be represented in type 'int'
Fixes: 15310/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FOURXM_fuzzer-
5737051745419264
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit
2bbea155bf7c6ce6d5ae53cc41e44798cad2f39c)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>