Added another catcher for an KeyError in the request participants callback

plugins/admidio_events/admidio_events.py

@@ -282,6 +282,7 @@ class Plugin:
             room.send_html(self.messages['info_event_id_err'])
             return
 
+        try:
             # Set header
             html_message = self.messages['event_participants_head'].format(
                 len(self.adm.events[id_event].getAllAttend()),
@@ -329,6 +330,8 @@ class Plugin:
             html_message += "</ul>"
 
             room.send_html(html_message)
+        except KeyError:
+            room.send_html(self.messages['unknown_event'])
 
     def chat_callback(self, room, event):
         room.send_text("Chat")