Do not recalculate default session when anonymous user changes his presence priority. JM-304

git-svn-id: http://svn.igniterealtime.org/svn/repos/messenger/branches@1495 b35dd754-fafc-0310-a699-88a17e54d16e

jive_messenger_2_1_branch/src/java/org/jivesoftware/messenger/SessionManager.java

@@ -521,6 +521,10 @@ public class SessionManager extends BasicModule {
      * @param priority The new priority for the session
      */
     public void changePriority(JID sender, int priority) {
+        if (sender.getNode() == null) {
+                // Do nothing if the session belongs to an anonymous user
+            return;
+        }
         String username = sender.getNode().toLowerCase();
         synchronized (username.intern()) {
             SessionMap resources = sessions.get(username);