Intended to replace https://patchwork.ffmpeg.org/project/ffmpeg/patch/20230802000135.26482-3-michael@niedermayer.cc/
with a more accurate block decoding magnitude bound.

Fixes: 62433/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5828618092937216
Fixes: 58299/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5828618092937216
Previous-version-reviewed-by: Tomas Härdin <git@haerdin.se>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>