fix: windows version (#72)

ui/flutter/windows/runner/flutter_window.cpp

@@ -26,6 +26,11 @@ bool FlutterWindow::OnCreate() {
   }
   RegisterPlugins(flutter_controller_->engine());
   SetChildContent(flutter_controller_->view()->GetNativeWindow());
+
+  flutter_controller_->engine()->SetNextFrameCallback([&]() {
+    this->Show();
+  });
+
   return true;
 }