Fixes: signed integer overflow: -277109688 * 8 cannot be represented in type 'int'
Fixes: 376118159/clusterfuzz-testcase-minimized-ffmpeg_SWR_fuzzer-5884436320681984
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>