Fix StreamManagement.Failed.toXML()

Note that this method is currently not used by Smack, as XMPP clients
usually do not emit that Nonza.

smack-tcp/src/main/java/org/jivesoftware/smack/sm/packet/StreamManagement.java

@@ -225,10 +225,11 @@ public class StreamManagement {
             if (condition == null && textElements.isEmpty()) {
                 xml.closeEmptyElement();
             } else {
-                xml.rightAngleBracket();
                 if (condition != null) {
+                    xml.rightAngleBracket();
                     xml.append(condition.toString());
                     xml.xmlnsAttribute(StanzaError.NAMESPACE);
+                    xml.closeEmptyElement();
                 }
                 xml.append(textElements);
                 xml.closeElement(ELEMENT);