avcodec/jpeg2000dwt: Fix runtime error: left shift of negative value -123

Fixes: 2208/clusterfuzz-testcase-minimized-5976593765761024

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