handle index out of range

maildir_gtd/app.py

@@ -225,7 +225,7 @@ class EmailViewerApp(App):
     def on_list_view_selected(self, event: ListView.Selected) -> None:
         """Called when an item in the list view is selected."""
         # logging.info(f"Selected item: {self.all_envelopes[event.list_view.index]}")
-        if (self.all_envelopes[event.list_view.index].get('type') == "header"):
+        if self.all_envelopes[event.list_view.index] is None or self.all_envelopes[event.list_view.index].get("type") == "header":
             # If the selected item is a header, do not change the current message ID
             return
         self.current_message_id = int(self.all_envelopes[event.list_view.index]['id'])