Fixes: signed integer overflow: -1082982400 + -1195645138 cannot be represented in type 'int'
Fixes: 376136843/clusterfuzz-testcase-minimized-ffmpeg_SWS_fuzzer-4791844321427456
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>