Fix issue in twitch presence checker

[4Kaylum]

Unhandled exception in internal background task 'twitch_follower_checker_loop'.
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/discord/ext/tasks/__init__.py", line 101, in _loop
    await self.coro(*args, **kwargs)
  File "/root/Apple.Py/cogs/twitch_follower_updater.py", line 46, in twitch_follower_checker_loop
    new_follower_list, new_cursor_value = await self.get_new_followers(row['twitch_bearer_token'], row['twitch_user_id'], row['twitch_cursor'])
  File "/root/Apple.Py/cogs/twitch_follower_updater.py", line 84, in get_new_followers
    async with self.bot.session.get(self.TWITCH_USER_FOLLOWS_URL, params=params, headers=headers) as r:
  File "/usr/local/lib/python3.6/dist-packages/aiohttp/client.py", line 1117, in __aenter__
    self._resp = await self._coro
  File "/usr/local/lib/python3.6/dist-packages/aiohttp/client.py", line 513, in _request
    traces=traces,
  File "/usr/local/lib/python3.6/dist-packages/aiohttp/client_reqrep.py", line 283, in __init__
    url2 = url.with_query(params)
  File "/usr/local/lib/python3.6/dist-packages/yarl/_url.py", line 983, in with_query
    new_query = self._get_str_query(*args, **kwargs)
  File "/usr/local/lib/python3.6/dist-packages/yarl/_url.py", line 944, in _get_str_query
    query = "&".join(self._query_seq_pairs(quoter, query.items()))
  File "/usr/local/lib/python3.6/dist-packages/yarl/_url.py", line 907, in _query_seq_pairs
    yield quoter(key) + "=" + quoter(cls._query_var(val))
  File "/usr/local/lib/python3.6/dist-packages/yarl/_url.py", line 925, in _query_var
    "of type {}".format(v, cls)
TypeError: Invalid variable type: value should be str, int or float, got None of type <class 'NoneType'>