fix: setState callback must not return the reload future

Signed-off-by: flemming-it <sf@flemming.it>

lib/src/flow_editor_page.dart

@@ -218,7 +218,10 @@ class _FlowEditorPageState extends State<FlowEditorPage>
     // change what the list must show.
     if (widget.flowsDir != old.flowsDir ||
         !setEquals(widget.sampleFlowNames, old.sampleFlowNames)) {
-      setState(() => _files = _listFiles());
+      final fresh = _listFiles();
+      setState(() {
+        _files = fresh;
+      });
     }
   }