Fix serveral issues on Linux environments

1. fix the crash issue in ComboBox
2. fix the network agent directory not correct issue
3. fix the first 3d tab switch failed issue
4. fix the filemenu not correct issue

Change-Id: I6a99218c0f7edbd57114ca1d9ff8c5c020d26d94
(cherry picked from commit b5e1b06af42aea9d1413be29dd58150b2ac8d470)

src/slic3r/GUI/GUI_App.cpp

@@ -2228,11 +2228,11 @@ bool GUI_App::on_init_inner()
 
         // An ugly solution to GH #5537 in which GUI_App::init_opengl (normally called from events wxEVT_PAINT
         // and wxEVT_SET_FOCUS before GUI_App::post_init is called) wasn't called before GUI_App::post_init and OpenGL wasn't initialized.
-#ifdef __linux__
-        if (!m_post_initialized && m_opengl_initialized) {
-#else
+//#ifdef __linux__
+//        if (!m_post_initialized && m_opengl_initialized) {
+//#else
         if (!m_post_initialized) {
-#endif
+//#endif
             m_post_initialized = true;
 #ifdef WIN32
             this->mainframe->register_win32_callbacks();