Fix CSG Path Polygon cache being removed after connect

fixes #30229

(cherry picked from commit bab36f12737769dd5f5c876731bc334323a4c5d2)

modules/csg/csg_shape.cpp

@@ -1832,7 +1832,6 @@ CSGBrush *CSGPolygon::_build_brush() {
 
 			path_cache->connect("tree_exited", this, "_path_exited");
 			path_cache->connect("curve_changed", this, "_path_changed");
-			path_cache = NULL;
 		}
 		curve = path->get_curve();
 		if (curve.is_null()) {