Fixed issue in network/images.js where load() would return undefined if image was already loaded

lib/network/Images.js

@@ -23,10 +23,11 @@ Images.prototype.setOnloadCallback = function(callback) {
  * @return {Image} img          The image object
  */
 Images.prototype.load = function(url, brokenUrl) {
-  if (this.images[url] == undefined) {
+  var img = this.images[url];
+  if (img === undefined) {
     // create the image
     var me = this;
-    var img = new Image();
+    img = new Image();
     img.onload = function () {
 
       // IE11 fix -- thanks dponch!