Fix (unreported) potentially giant memory leak in Cloth collision solver.

Not freeing its BVHTree in case there were no collision objects,
could quickly lead to hundreds of MB of memleak!

source/blender/blenkernel/intern/collision.c

@@ -1357,6 +1357,7 @@ void cloth_find_point_contacts(Object *ob, ClothModifierData *clmd, float step,
 	if (!collobjs) {
 		*r_collider_contacts = NULL;
 		*r_totcolliders = 0;
+		BLI_bvhtree_free(cloth_bvh);
 		return;
 	}