grloadac.cpp: Do not render windows in interior view

This commit forces OpenGL to cull the windows when loading the model, so
that single-sided windows are not rendered in interior view.

Cherry-picked from:

- https://sourceforge.net/p/cars-sports-racing/code/303/
- https://sourceforge.net/p/cars-sports-racing/code/308/


git-svn-id: https://svn.code.sf.net/p/speed-dreams/code/trunk@9556 30fe4595-0a0c-4342-8851-515496e4dcbd

Former-commit-id: bd67efd9ec4a2a7b65b32799e1c24fb1f3dee02d
Former-commit-id: d43554e9fa2a7a66d0c5765a108cb4c6e7b96d6f

src/modules/graphic/ssggraph/grloadac.cpp

@@ -253,6 +253,7 @@ static ssgState *get_simple_state ( _ssgMaterial *mat )
 
   if (isawindow)
   {
+      st->enable (GL_CULL_FACE);
       st->enable  ( GL_BLEND );
       st->setTranslucent () ;
   }