Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_DXA_fuzzer-5730576523198464
Fixes: signed integer overflow: 2147483566 + 82 cannot be represented in type 'int'

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