only send once

matrix_gpt/bot/callbacks.py

@@ -77,6 +77,7 @@ class Callbacks:
             for event in thread_content:
                 if isinstance(event, MegolmEvent):
                     await send_text_to_room(self.client, room.room_id, 'Decryption Failure', reply_to_event_id=event.event_id, thread=True, thread_root_id=thread_content[0].event_id)
+                    return
                 else:
                     api_data.append({
                         'role': 'assistant' if event.sender == self.client.user_id else 'user',