Added forceZero method and used it

Author: photonstorm

src/renderer/webgl/PipelineManager.js

@@ -489,6 +489,11 @@ var PipelineManager = new Class({
         );
     },
 
+    forceZero: function ()
+    {
+        return (this.current && this.current.forceZero);
+    },
+
     /**
      * Sets the Multi Pipeline to be the currently bound pipeline.
      *

src/renderer/webgl/WebGLRenderer.js

@@ -1258,7 +1258,7 @@ var WebGLRenderer = new Class({
      */
     setTextureSource: function (textureSource)
     {
-        if (this.pipelines.current.forceZero)
+        if (this.pipelines.forceZero())
         {
             this.setTextureZero(textureSource.glTexture, true);
 
@@ -1494,7 +1494,7 @@ var WebGLRenderer = new Class({
      */
     setTexture2D: function (texture)
     {
-        if (this.pipelines.current.forceZero)
+        if (this.pipelines.forceZero())
         {
             this.setTextureZero(texture, true);