Suppress underscore errors when not on the right page. Ideally page specific JS…

Suppress underscore errors when not on the right page. Ideally page specific JS execution would take care of this.

lms/static/coffee/src/discussion/views/discussion_thread_list_view.coffee

 if Backbone?
   class @DiscussionThreadListView extends Backbone.View
-    template: _.template($("#thread-list-template").html())
     events:
       "click .search": "showSearch"
       "click .browse": "toggleTopicDrop"
@@ -17,6 +16,7 @@ if Backbone?
       @sidebar_padding = 10
       @sidebar_header_height = 87
       @boardName
+      @template = _.template($("#thread-list-template").html())
 
     reloadDisplayedCollection: (thread) =>
       thread_id = thread.get('id')