y2: fix some bug

1. Fixed a bug where the login window was not destroyed when switching languages;
2. Fixed the display issue when the model does not have the corresponding picture;
3. Fix button display problem when the local device has no IP address.

src/slic3r/GUI/GUI_App.hpp

@@ -201,6 +201,7 @@ public:
     // Process command line parameters cached in this->init_params,
     // load configs, STLs etc.
     void            post_init();
+    void            shutdown();
     // If formatted for github, plaintext with OpenGL extensions enclosed into <details>.
     // Otherwise HTML formatted for the system info dialog.
     static std::string get_gl_info(bool for_github);