Fix crash in q3bsp loading on submodels where it was adding the submodelsurfaces_star...

Fix crash in q3bsp loading on submodels where it was adding the submodelsurfaces_start and shouldn't (reported by Cloudwalk - thanks).

Fix missing submodels in q3bsp loading where it was allocating a separate modelsurfaces_sorted for each submodel which was probably coming out uninitialized.

Simplified Mod_MakeSortedSurfaces a little by sorting each submodel separately - no need to worry about sorting by submodel this way, they're going to stay in the same ranges.

Refactored away the many duplicates of the mod->DrawSky and mod->DrawAddWaterPlanes setting code into Mod_SetDrawSkyAndWater function which is called after loader (and in submodel creation), this also means it checks for NULL texture pointer consistently whereas that varied a bit in the past by loader.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@13079 d7cf8633-e32d-0410-b094-e92efae38249