Fix (harmless) uninitialized memory usage in BVH binning.

Fix unneeded warnings with c++ guardedalloc, delete NULL is valid.

intern/cycles/bvh/bvh_binning.cpp

@@ -122,6 +122,7 @@ BVHObjectBinning::BVHObjectBinning(const BVHRange& job, BVHReference *prims)
 		bx = merge(bx,bin_bounds[i][0]); r_area[i][0] = bx.half_area();
 		by = merge(by,bin_bounds[i][1]); r_area[i][1] = by.half_area();
 		bz = merge(bz,bin_bounds[i][2]); r_area[i][2] = bz.half_area();
+		r_area[i][3] = r_area[i][2];
 	}
 
 	/* sweep from left to right and compute SAH */

intern/guardedalloc/cpp/mallocn.cpp

@@ -41,5 +41,7 @@ void* operator new (size_t size, const char *str)
 
 void operator delete (void *p)
 {
-	MEM_freeN(p);
+	/* delete NULL is valid in c++ */
+	if(p)
+		MEM_freeN(p);
 }