Fix GC adapter not being detected when you enable controller in settings

GCAdapter::UseAdapter() reads s_is_adapter_wanted, which gets
initialized by config_guard.~ConfigChangeCallbackGuard(). So we must
wait until after destroying the config guard to know whether we have any
controllers set to GC Adapter.

Source/Core/DolphinQt/Config/GamecubeControllersWidget.cpp

@@ -198,12 +198,11 @@ void GamecubeControllersWidget::SaveSettings()
                                                                       static_cast<s32>(i));
       }
     }
-
-    if (GCAdapter::UseAdapter())
-      GCAdapter::StartScanThread();
-    else
-      GCAdapter::StopScanThread();
   }
+  if (GCAdapter::UseAdapter())
+    GCAdapter::StartScanThread();
+  else
+    GCAdapter::StopScanThread();
 
   SConfig::GetInstance().SaveSettings();
 }