fixed deadlock issue when providing invalid login info

deadlock is caused by calling xmpp->stop() when the client is not
connected yet. A simple check of the current state prevents this
problem.

src/ofxXMPP.cpp

@@ -85,7 +85,9 @@ void ofxXMPP::conn_handler(xmpp_conn_t * const conn, const xmpp_conn_event_t sta
         	xmpp->mutex.unlock();
         }else{
         	xmpp->mutex.unlock();
-        	xmpp->stop();
+			if (((ofxXMPP*) userdata)->getConnectionState() == ofxXMPPConnected){ // without this check xmpp->stop will be caught in a deadlock
+				xmpp->stop();
+			}
         }
         xmpp->connectionState = ofxXMPPDisconnected;
     }