Qt: Restore render widget size and position

Source/Core/DolphinQt2/MainWindow.h

@@ -193,5 +193,6 @@ private:
   RegisterWidget* m_register_widget;
   WatchWidget* m_watch_widget;
   CheatsManager* m_cheats_manager;
-  QSize m_render_widget_size{640, 480};
+  QSize m_render_widget_size;
+  QPoint m_render_widget_position;
 };