about: dialog does not display correctly when re-opened

Fixes: #7129
The help dialog was not rendering the list of extensions, hence functionality was added to display the list even after it being closed once.

Signed-off-by: Muhammad Anas Shahid <muhammad.shahid@ericsson.com>

packages/core/src/browser/about-dialog.tsx

@@ -19,6 +19,7 @@ import { inject, injectable, postConstruct } from 'inversify';
 import { DialogProps } from './dialogs';
 import { ReactDialog } from './dialogs/react-dialog';
 import { ApplicationServer, ApplicationInfo, ExtensionInfo } from '../common/application-protocol';
+import { Message } from './widgets/widget';
 
 export const ABOUT_CONTENT_CLASS = 'theia-aboutDialog';
 export const ABOUT_EXTENSIONS_CLASS = 'theia-aboutExtensions';
@@ -79,5 +80,10 @@ export class AboutDialog extends ReactDialog<void> {
         </div>;
     }
 
+    protected onAfterAttach(msg: Message): void {
+        super.onAfterAttach(msg);
+        this.update();
+    }
+
     get value(): undefined { return undefined; }
 }