prevent looping on fetchToken()

bigbluebutton-html5/imports/ui/components/join-handler/component.jsx

@@ -33,14 +33,21 @@ class JoinHandler extends Component {
   }
 
   componentDidMount() {
+    this._isMounted = true;
     this.fetchToken();
   }
 
+  componentWillUnmount() {
+    this._isMounted = false;
+  }
+
   changeToJoin(bool) {
     this.setState({ joined: bool });
   }
 
   async fetchToken() {
+    if (!this._isMounted) return;
+
     if (!Meteor.status().connected) {
       if (this.numFetchTokenRetries > 9) {
         logger.error({