ref(dialog): set mounted flag after mount

react/features/base/dialog/components/AbstractDialog.js

     }
 
     /**
-     * Implements React's {@link Component#componentWillMount()}. Invoked
+     * Implements React's {@link Component#componentDidMount()}. Invoked
      * immediately before mounting occurs.
      *
      * @inheritdoc
      */
-    componentWillMount() {
+    componentDidMount() {
         this._mounted = true;
     }