Don't create AP items for empty networks

Current code is sometime attempting to create menu items for wifi
networks that have no visible AP. I have no idea why this is
happening, but it should fix the symptoms and avoid exceptions.

https://bugzilla.gnome.org/show_bug.cgi?id=658150

js/ui/status/network.js

@@ -1480,6 +1480,11 @@ NMDeviceWireless.prototype = {
     },
 
     _createNetworkItem: function(apObj, position) {
+        if(!apObj.accessPoints || apObj.accessPoints.length == 0) {
+            // this should not happen, but I have no idea why it happens
+            return;
+        }
+
         if(apObj.connections.length > 0) {
             if (apObj.connections.length == 1)
                 apObj.item = this._createAPItem(apObj.connections[0], apObj, false);