Fixed advanced installation mode crash

source/ubinstall-gtk-advanced.c

@@ -700,8 +700,8 @@ void yon_advanced_init(main_window *widgets){
     }
     yon_char_parsed_free(vmf_file,size);
     g_signal_handlers_unblock_by_func(G_OBJECT(widgets->AdvancedVirtualDeviceCombo),G_CALLBACK(on_advanced_virtual_device_changed),widgets);
-
-    if (!strcmp(config(AUTOINSTALL_TYPE_INSTALL),"custom")){
+    char *install_mode = config(AUTOINSTALL_TYPE_INSTALL);
+    if (!yon_char_is_empty(install_mode)&&!strcmp(install_mode,"custom")){
         advanced_part_data *data1 = yon_advanced_get_config_data(0);
         advanced_part_data *data2 = yon_advanced_get_config_data(1);
         yon_advanced_part_select_for_data(data1,widgets);