Error when checking starboard message

If `check_exists_starboard_message` is called when the message to check is on the starboard, it will throw the following error:
```
Ignoring exception in on_raw_reaction_add
Traceback (most recent call last):
File "/home/user/.local/lib/python3.9/site-packages/discord/client.py", line 343, in _run_event
await coro(*args, **kwargs)
File "/home/user/tle/cogs/starboard.py", line 35, in on_raw_reaction_add
await self.check_and_add_to_starboard(starboard_channel_id, payload)
File "/home/user/tle/cogs/starboard.py", line 99, in check_and_add_to_starboard
if self.db.check_exists_starboard_message(message.id):
File "/home/user/tle/util/db/user_db_conn.py", line 481, in check_exists_starboard_message
res = self.conn.execute(query, (original_msg_id,)).fetchone()
File "/home/user/tle/util/db/user_db_conn.py", line 60, in namedtuple_factory
return Row(*row)
TypeError: () takes 1 positional argument but 2 were given
```

This is probably caused by the query `SELECT 1 FROM starboard_message WHERE original_msg_id = ?` ([source](https://github.com/cheran-senthil/TLE/blob/master/tle/util/db/user_db_conn.py#L478-L480)): if it returns a row, then there would have a column named `1`, which is not an identifier and makes [`namedtuple_factory`](https://github.com/cheran-senthil/TLE/blob/master/tle/util/db/user_db_conn.py#L58) create an incorrect number of fields.

Start in tle/util/db/user_db_conn.py at check_exists_starboard_message and inspect namedtuple_factory, then follow the call from tle/cogs/starboard.py. Reproduce the check for a message already on the starboard and confirm the query result no longer raises the reported TypeError.

Written by the indexing model from the issue text.