Fixes: signed integer overflow: 2099257366 * 2 cannot be represented in type 'int'
Fixes: 27486/clusterfuzz-testcase-minimized-ffmpeg_dem_FOURXM_fuzzer-5112179134824448

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