Bugfix #5399

Irregular Shadow Buffer: doesn't support wire shadow, but also should not
crash then!
Note that ISB works with real face coverage, not zbuffering faces at all.
For wires to work in this method, we have to introduce a wire thickness,
but that will give endpoint condition troubles.

source/blender/render/intern/source/shadbuf.c

@@ -1432,6 +1432,7 @@ static void isb_bsp_fillfaces(Render *re, LampRen *lar, ISBBranch *root)
 			ma= vlr->mat;
 			ok= 1;
 			if((ma->mode & MA_SHADBUF)==0) ok= 0;
+			if(ma->mode & MA_WIRE) ok= 0;
 			zspanstrand.shad_alpha= zspan.shad_alpha= ma->shad_alpha;
 		}