minor changes, clean-up

[gcode-importer]

Originally reported on Google Code with ID 349

From https://code.google.com/p/sumatrapdf/source/browse/trunk/ext/_patches/openjpeg.patch?spec=svn8835&r=8834
:

* Replace magic number 32 in j2k.c@3167 with ABI-change-proof calculation |sizeof(l_tcp->pocs)
/ sizeof(l_tcp->pocs[0])|.

* Replace stdin-spamming printf in t2.c@866 with fprintf(stderr, ...) or remove it
altogether in t2.c@870.

* Reset l_cblk->data in t2.c@1161 so that it isn't accidentally double-freed later
on.

* Also, apparently MSVC debug CRT's memory manager asserts even for (size_t)-0x100
and the actual maximum allocation size is 0x7ffdefff for opj_malloc.h (three times).

Reported by zeniko on 2014-05-15 20:59:20

[rouault]

I only took into account the suggestion related to the max number of POCs. Can't make sense of other ones with current code, or already taken into account since.