Fix two memory allocation issues

Fix two memory allocation issues

In fa06dd40f48b20d738b6bd604758c81defd76cfd I misunderstood the
subdivision code, causing sentinel2 to be written past the end of the
buffer... somehow many maps and games worked fine despite this. This
commit reverts the bad line from that commit.

A very old (div0-stable) bug when loading Q1BSP meant we didn't allocate
enough texture memory when a "sky" texture name wasn't all lowercase,
causing a crash when loading custom map e2m9.

Signed-off-by: bones_was_here <bones_was_here@xonotic.au>