avcodec/hqxdsp: Fix multiple runtime error: signed integer overflow: 248220 * 21407 cannot be represented in type 'int' in idct_col()

Fixes: 1405/clusterfuzz-testcase-minimized-5011491835084800

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