Show a message when expenses list is empty

moneymgr_mobile/lib/routes/scans_list/scans_list_screen.dart

@@ -48,6 +48,12 @@ class _ExpensesList extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    if (list.isEmpty) {
+      return const Center(
+        child: Text("There is no entry waiting for upload (yet)"),
+      );
+    }
+
     return ListView.builder(
       itemBuilder: (context, entryNum) {
         final expense = list[entryNum];

moneymgr_mobile/lib/widgets/synchronize_button.dart

@@ -40,9 +40,9 @@ Future<void> _performSynchronization(Ref ref) async {
 
     // Lastly delete the local expense
     ref.watch(expensesProvider).requireValue.deleteExpense(exp);
-
-    ref.invalidate(expensesProvider);
   }
+
+  ref.invalidate(expensesProvider);
 }
 
 class SynchronizeButton extends HookConsumerWidget {