fixed ui error when deleting items

lib/pages/dashboard_page.dart

@@ -89,7 +89,9 @@ class _DashboardPageState extends State<DashboardPage> {
   void _onDeleteTapped() {
     DbHelper.deleteChecklistByid(
         checklists.elementAt(_selectedChecklistIndex!).id);
+    setState(() {
       _selectedChecklistIndex = null;
+    });
   }
 
   @override