avcodec/svq3: Fix multiple runtime error: signed integer overflow: -237341 * 24552 cannot be represented in type 'int'

Fixes: 1429/clusterfuzz-testcase-minimized-5959951610544128

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