FIX: shutdown GUI_App after confirm dialog

Change-Id: Ie379e9e764f43be1592a74b929bfbfc1d2d41a49
Signed-off-by: Stone Li <stone.li@bambulab.com>

src/slic3r/GUI/MainFrame.cpp

@@ -700,6 +700,7 @@ void MainFrame::shutdown()
     // to avoid any manipulations with them from App->wxEVT_IDLE after of the mainframe closing
     wxGetApp().tabs_list.clear();
     wxGetApp().model_tabs_list.clear();
+    wxGetApp().shutdown();
     // BBS: why clear ?
     //wxGetApp().plater_ = nullptr;
 }