Fix for bug #7787: QMC AO could give bad results tracing rays from an

untraceable material, cause is that the ray start position got set
only once, but it needs to be set for each ray since it can be clipped
to the octree bounding box.

source/blender/render/intern/source/rayshade.c

@@ -1505,7 +1505,6 @@ void ray_ao_qmc(ShadeInput *shi, float *shadfac)
 	isec.ob_last= 0;
 	isec.mode= (R.wrld.aomode & WO_AODIST)?RE_RAY_SHADOW_TRA:RE_RAY_SHADOW;
 	isec.lay= -1;
-	VECCOPY(isec.start, shi->co);
 	
 	shadfac[0]= shadfac[1]= shadfac[2]= 0.0f;
 	
@@ -1558,6 +1557,7 @@ void ray_ao_qmc(ShadeInput *shi, float *shadfac)
 		
 		Normalize(dir);
 			
+		VECCOPY(isec.start, shi->co);
 		isec.end[0] = shi->co[0] - maxdist*dir[0];
 		isec.end[1] = shi->co[1] - maxdist*dir[1];
 		isec.end[2] = shi->co[2] - maxdist*dir[2];