fix prebind reference error

converse.js

@@ -4580,7 +4580,7 @@
                         rid += 1;
                         this.session.save({rid: rid}); // The RID needs to be increased with each request.
                         this.connection.attach(jid, sid, rid, this.onConnect);
-                    } else if (prebind) {
+                    } else if (this.prebind) {
                         delete this.connection;
                         this.emit('noResumeableSession');
                     }