avcodec/jpeg2000dec: Allocate lengthinc and data_start arrays as needed

Decreases memory requirements
Fixes: OOM
Fixes: 4525/clusterfuzz-testcase-minimized-6400713073623040

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