Disable self.lst_files widget when setting UI to busy state

Author: seiya-git

pspdocmaker_gui.py

@@ -857,6 +857,7 @@ def _on_render_done(self, pages, for_file):
     def _set_ui_busy(self, busy: bool):
         for btn in (
             # files / folders
+            self.lst_files,
             self.btn_add_files,
             self.btn_add_folder,
             self.btn_remove,