avcodec/jpeg2000dwt: Fix integer overflow in dwt_decode97_int()

Fixes: runtime error: signed integer overflow: -163654656 * 256 cannot be represented in type 'int'
Fixes: 2367/clusterfuzz-testcase-minimized-4648678897745920

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