Fix refresh functionality

lib/home_page.dart

@@ -191,6 +191,9 @@ class _MyHomePageState extends State<MyHomePage> with RouteAware {
         child: FutureBuilder(
           future: sheets,
           builder: (BuildContext context, AsyncSnapshot<List<Sheet>> snapshot) {
+            if (snapshot.connectionState != ConnectionState.done) {
+              return const Center(child: CircularProgressIndicator());
+            }
             if (snapshot.hasData) {
               return SheetsWidget(
                 sheets: snapshot.data!,