Do not display "auth failed" modal on clean posts.

Refs #4543
- Check EditorController.isDirty before displaying the
  authorization failed modal dialog.  This prevents the modal
  appearing immediately upon entering the editor in cases where
  auth has failed prior to opening the editor.

core/client/routes/application.js

@@ -20,12 +20,16 @@ var ApplicationRoute = Ember.Route.extend(SimpleAuth.ApplicationRouteMixin, Shor
 
     actions: {
         authorizationFailed: function () {
-            var currentRoute = this.get('controller').get('currentRouteName');
+            var currentRoute = this.get('controller').get('currentRouteName'),
+                editorController;
 
             if (currentRoute.split('.')[0] === 'editor') {
-                this.send('openModal', 'auth-failed-unsaved', this.controllerFor(currentRoute));
+                editorController = this.controllerFor(currentRoute);
 
-                return;
+                if (editorController.get('isDirty')) {
+                    this.send('openModal', 'auth-failed-unsaved', editorController);
+                    return;
+                }
             }
 
             this._super();