Fix two bugs found by @TiuTalk

* When redirecting internal links, double-check that they actually
  are internal before doing so.
* Avoid double-adding items to the /browse mod list

src/coffee/controllers/browse_page_controller.coffee

@@ -45,6 +45,7 @@ module.exports = class BrowsePageController extends PageController
             controller = @_controllers[controllerIndex]
             if not controller?
                 controller = new ModController model:mod
+                @_controllers.push controller
                 controller.render()
                 @$modContainer.append controller.$el
             else