.renderOrder does not work - #5496

#5496 introduced a check for .renderOrder in painterSortStable. This is a property of the webglObject. It is never copied from the Object3D where it is defined and thus it does not work:

https://github.com/mrdoob/three.js/commit/052f81ab6ed877935ad4657453752e9efa8018a4

The fix is to copy the property over when sorting and define it in webglObject as well.

src/renderers/WebGLRenderer.js

@@ -3467,6 +3467,7 @@ THREE.WebGLRenderer = function ( parameters ) {
 							_vector3.applyProjection( _projScreenMatrix );
 
 							webglObject.z = _vector3.z;
+							webglObject.renderOrder = object.renderOrder;
 
 						}
 
@@ -3887,7 +3888,8 @@ THREE.WebGLRenderer = function ( parameters ) {
 				buffer: buffer,
 				object: object,
 				material: null,
-				z: 0
+				z: 0,
+				renderOrder: 0
 			}
 		);
 
@@ -3901,7 +3903,8 @@ THREE.WebGLRenderer = function ( parameters ) {
 				object: object,
 				opaque: null,
 				transparent: null,
-				z: 0
+				z: 0,
+				renderOrder: 0
 			}
 		);