FS-11279: Wrap verto.clientReady message callback in check for onMessage callback function

The verto.clientReady event calls the onMessage callback function passed in
the Verto object. We should check for the existence of this callback function
before trying to call it.

html5/verto/js/src/jquery.verto.js

@@ -613,7 +613,9 @@
                 break;
 
             case 'verto.clientReady':
-                verto.callbacks.onMessage(verto, null, $.verto.enum.message.clientReady, data.params);
+                if (verto.callbacks.onMessage) {
+                    verto.callbacks.onMessage(verto, null, $.verto.enum.message.clientReady, data.params);
+                }
                 console.debug("CLIENT READY", data.params);
                 break;