Fixed (Raw)ShaderMaterial clone(). See #6309.

src/materials/ShaderMaterial.js

@@ -76,9 +76,9 @@ THREE.ShaderMaterial = function ( parameters ) {
 THREE.ShaderMaterial.prototype = Object.create( THREE.Material.prototype );
 THREE.ShaderMaterial.prototype.constructor = THREE.ShaderMaterial;
 
-THREE.ShaderMaterial.prototype.clone = function () {
+THREE.ShaderMaterial.prototype.clone = function ( material ) {
 
-	var material = new THREE.ShaderMaterial();
+	if ( material === undefined ) material = new THREE.ShaderMaterial();
 
 	THREE.Material.prototype.clone.call( this, material );