Properly handle empty CSGShapes

(cherry picked from commit 24a6aac472d3d57bb0720c5ac46a98856e3bd5e0)

modules/csg/csg_shape.cpp

@@ -715,9 +715,9 @@ CSGPrimitive::CSGPrimitive() {
 /////////////////////
 
 CSGBrush *CSGMesh::_build_brush() {
-
-	if (!mesh.is_valid())
-		return NULL;
+	if (!mesh.is_valid()) {
+		return memnew(CSGBrush);
+	}
 
 	PoolVector<Vector3> vertices;
 	PoolVector<bool> smooth;
@@ -735,7 +735,7 @@ CSGBrush *CSGMesh::_build_brush() {
 
 		if (arrays.size() == 0) {
 			_make_dirty();
-			ERR_FAIL_COND_V(arrays.size() == 0, NULL);
+			ERR_FAIL_COND_V(arrays.size() == 0, memnew(CSGBrush));
 		}
 
 		PoolVector<Vector3> avertices = arrays[Mesh::ARRAY_VERTEX];
@@ -860,8 +860,9 @@ CSGBrush *CSGMesh::_build_brush() {
 		}
 	}
 
-	if (vertices.size() == 0)
-		return NULL;
+	if (vertices.size() == 0) {
+		return memnew(CSGBrush);
+	}
 
 	return _create_brush_from_arrays(vertices, uvs, smooth, materials);
 }
@@ -1544,8 +1545,9 @@ CSGBrush *CSGTorus::_build_brush() {
 	float min_radius = inner_radius;
 	float max_radius = outer_radius;
 
-	if (min_radius == max_radius)
-		return NULL; //sorry, can't
+	if (min_radius == max_radius) {
+		return memnew(CSGBrush); //sorry, can't
+	}
 
 	if (min_radius > max_radius) {
 		SWAP(min_radius, max_radius);
@@ -1769,8 +1771,9 @@ CSGBrush *CSGPolygon::_build_brush() {
 
 	// set our bounding box
 
-	if (polygon.size() < 3)
-		return NULL;
+	if (polygon.size() < 3) {
+		return memnew(CSGBrush);
+	}
 
 	Vector<Point2> final_polygon = polygon;
 
@@ -1780,8 +1783,9 @@ CSGBrush *CSGPolygon::_build_brush() {
 
 	Vector<int> triangles = Geometry::triangulate_polygon(final_polygon);
 
-	if (triangles.size() < 3)
-		return NULL;
+	if (triangles.size() < 3) {
+		return memnew(CSGBrush);
+	}
 
 	Path *path = NULL;
 	Ref<Curve3D> curve;
@@ -1805,14 +1809,17 @@ CSGBrush *CSGPolygon::_build_brush() {
 	Vector2 final_polygon_size = final_polygon_max - final_polygon_min;
 
 	if (mode == MODE_PATH) {
-		if (!has_node(path_node))
-			return NULL;
+		if (!has_node(path_node)) {
+			return memnew(CSGBrush);
+		}
 		Node *n = get_node(path_node);
-		if (!n)
-			return NULL;
+		if (!n) {
+			return memnew(CSGBrush);
+		}
 		path = Object::cast_to<Path>(n);
-		if (!path)
-			return NULL;
+		if (!path) {
+			return memnew(CSGBrush);
+		}
 
 		if (path != path_cache) {
 			if (path_cache) {
@@ -1828,10 +1835,12 @@ CSGBrush *CSGPolygon::_build_brush() {
 			path_cache = NULL;
 		}
 		curve = path->get_curve();
-		if (curve.is_null())
-			return NULL;
-		if (curve->get_baked_length() <= 0)
-			return NULL;
+		if (curve.is_null()) {
+			return memnew(CSGBrush);
+		}
+		if (curve->get_baked_length() <= 0) {
+			return memnew(CSGBrush);
+		}
 	}
 	CSGBrush *brush = memnew(CSGBrush);