Another fix to thread update

boards/static/js/thread_update.js

@@ -27,7 +27,6 b" var wsUrl = 'ws://localhost:9090/connect"
 var wsUser = '';
 
 var loading = false;
-var lastUpdateTime = null;
 var unreadPosts = 0;
 var documentOriginalTitle = '';
 
@@ -82,9 +81,9 b' function connectWebsocket() {'
  * missed.
  */
 function getThreadDiff() {
-    var diffUrl = '/api/diff_thread/' + threadId + '/' + lastUpdateTime + '/';
+    var lastUpdateTime = $('.metapanel').attr('data-last-update');
 
-    lastUpdateTime = $('.metapanel').attr('data-last-update');
+    var diffUrl = '/api/diff_thread/' + threadId + '/' + lastUpdateTime + '/';
 
     $.getJSON(diffUrl)
         .success(function(data) {
@@ -110,8 +109,6 b' function getThreadDiff() {'
             }
 
             // TODO Process removed posts if any
-
-            lastUpdateTime = data.last_update;
         })
 }