Singlee: Only attempt to show GUI if plugin has one

source/bridges/CarlaBridgePlugin.cpp

@@ -523,7 +523,12 @@ int main(int argc, char* argv[])
         else
         {
             carla_set_active(0, true);
-            carla_show_gui(0, true);
+
+            if (const CarlaPluginInfo* const pluginInfo = carla_get_plugin_info(0))
+            {
+                if (pluginInfo->hints & CarlaBackend::PLUGIN_HAS_GUI)
+                    carla_show_gui(0, true);
+            }
         }
 
         client.ready();