submarine_swaps: fix swapserver dying taskgroup (follow-up 21e3fd9 and 4490bd3)

Author: ecdsa

electrum/submarine_swaps.py

@@ -1725,7 +1725,7 @@ async def check_direct_messages(self):
                         "error": str(e)[:100],
                         "reply_to": event.id,
                     })
-                    await self.send_direct_message(event.pubkey,[], error_response)
+                    await self.send_direct_message(event.pubkey, error_response)
             else:
                 self.logger.info(f'unknown message {content}')