avcodec/jpeg2000: Check that codsty->log2_prec_widths/heights has been initialized

Fixes: OOM
Fixes: 2225/clusterfuzz-testcase-minimized-5505632079708160

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