WebGLShadowMap: Avoid changing state when shadowMap is enabled but there are not light with shadows in the scene.

src/renderers/webgl/WebGLShadowMap.js

@@ -93,6 +93,9 @@ THREE.WebGLShadowMap = function ( _renderer, _lights, _objects ) {
 	this.render = function ( scene, camera ) {
 
 		var faceCount, isPointLight;
+		var shadows = _lights.shadows;
+
+		if ( shadows.length === 0 ) return;
 
 		if ( scope.enabled === false ) return;
 		if ( scope.autoUpdate === false && scope.needsUpdate === false ) return;
@@ -108,8 +111,6 @@ THREE.WebGLShadowMap = function ( _renderer, _lights, _objects ) {
 
 		// render depth map
 
-		var shadows = _lights.shadows;
-
 		for ( var i = 0, il = shadows.length; i < il; i ++ ) {
 
 			var light = shadows[ i ];