Make sure the pong handler is always registered.

https://github.com/jcbrand/converse.js/commit/47e00ae005fc4034836595d4267953b46a869cb7

converse.js

@@ -750,8 +750,8 @@
         };
 
         this.registerPingHandler = function () {
-            if (this.ping_interval > 0) {
             this.registerPongHandler();
+            if (this.ping_interval > 0) {
                 this.connection.addHandler(function () {
                     /* Handler on each stanza, saves the received date
                      * in order to ping only when needed.