Fixes: signed integer overflow: 175 + 2147483571 cannot be represented in type 'int'
Fixes: 26833/clusterfuzz-testcase-minimized-ffmpeg_dem_IMAGE2_fuzzer-5969501214212096

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