Fix sidebar height growing forever when loading more pages, and also jumping to…

Fix sidebar height growing forever when loading more pages, and also jumping to top when loading more pages.

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

@@ -112,13 +112,15 @@ if Backbone?
 
       @$(".post-list").html(rendered.html())
       @renderMorePages()
+      @updateSidebar()
       @trigger "threads:rendered"
 
     renderMorePages: ->
       if @displayedCollection.hasMorePages()
         @$(".post-list").append("<li class='more-pages'><a href='#'>Load more</a></li>")
 
-    loadMorePages: ->
+    loadMorePages: (event) ->
+      event.preventDefault()
       @$(".more-pages").html('<div class="loading-animation"></div>')
       @$(".more-pages").addClass("loading")
       @collection.retrieveAnotherPage(@current_search, @discussionIds, @sortBy)