Fixed possible NPE. JM-1082

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/trunk@8446 b35dd754-fafc-0310-a699-88a17e54d16e

src/java/org/jivesoftware/openfire/muc/spi/MUCRoomImpl.java

@@ -1380,7 +1380,7 @@ public class MUCRoomImpl implements MUCRoom {
             if (reason != null && reason.length() > 0) {
                 Element invite = frag.element("invite");
                 if (invite == null) {
-                    invite.addElement("invite");
+                    invite = frag.addElement("invite");
                 }
                 invite.addElement("reason").setText(reason);
             }