bsa::fo4::File::write_directx uses the wrong arraySize for cubemaps

[Ryan-rsm-McKenzie]

According to the docs, texture arrays for cubemaps are supposed to be a multiple of 6 in length. We currently write 1 unconditionally as the length. Hopefully someone who actually understands dds files can chime in to help use understand how to compute the correct number.

bsa/src/bsa/fo4.cpp

Line 745 in 2e16e3a

.arraySize = 1,