add scrollbar, improve presets, other small fixes

src/app_cloud.cpp

@@ -136,6 +136,8 @@ void App::cloud_browse()
 
     dialog->btn_ok->on_click = [this, dialog](Node*)
     {
+        if (dialog->selected_file.empty())
+            return;
         dialog->destroy();
         std::thread([this, dialog] {
             async_start();