avcodec/jpeg2000dec: Check bpno in decode_cblk()

Fixes: undefined shift
Fixes: c409ef86f892335a0a164b5871174d5a/asan_heap-oob_1dff564_2159_162b7234616deab02b544410455eb07b.mov

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
