avcodec/jpeg2000: fix type of arguments of tag_tree_size

Fixes: out of array read
Fixes: 36b8096fefab16c4c9326a508053e95c/signal_sigsegv_1d9ce18_3233_1a55196b018106dfabeace071a432d9e.r3d

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
