[gnome-shell] extensionPrefs: Add missing return value

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit dd1fdf88ff411518850f8e3b7ca49faf3d473653
Author: Florian Müllner <fmuellner gnome org>
Date:   Sun Jul 21 00:07:00 2019 +0200

    extensionPrefs: Add missing return value
    
    When commit a7ec7583aaa17 merged two functions into one, it left
    out the expected return value from one branch.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/635

 js/extensionPrefs/main.js | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/js/extensionPrefs/main.js b/js/extensionPrefs/main.js
index e5961e2e0..afac49a80 100644
--- a/js/extensionPrefs/main.js
+++ b/js/extensionPrefs/main.js
@@ -78,6 +78,8 @@ var Application = GObject.registerClass({
         dialog.set_default_size(600, 400);
         dialog.add(widget);
         dialog.show();
+
+        return true;
     }
 
     _buildErrorUI(row, exc) {