[bsp] incorrect texture coordinates on planar patches

[SomaZ]

The addon doesn't cull rows and colums. It uses controll points for interpolating texture coordinates which doesn't happen in id tech 3 because it culls the interpolated data on planar patches. This leads to false texture coordinates in the blender import.

[SomaZ]

I decided not to fix it. Its easy for a user to fix those issues with "limited disolve", but this will break patching patch meshes. Also, this is probably the slowest part of the code and checking for culling rows and columns would make it even slower. I will keep this issue open for people to see.