modalDialog: Consistently return correct boolean for open() in ModalDialogs

Previously these calls either ignored the return from super.open() or
implicitely returned false.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2038>

js/ui/runDialog.js

@@ -249,8 +249,8 @@ class RunDialog extends ModalDialog.ModalDialog {
         this._commandError = false;
 
         if (this._lockdownSettings.get_boolean(DISABLE_COMMAND_LINE_KEY))
-            return;
+            return false;
 
-        super.open();
+        return super.open();
     }
 });