Watch channels tries to get task result without first ensuring the task has finished

[MarkKoz]

Sentry Issue: BOT-70

InvalidStateError: Result is not set.
(1 additional frame(s) were not displayed)
...
  File "discord/ext/commands/bot.py", line 731, in reload_extension
    self._remove_module_references(lib.__name__)
  File "discord/ext/commands/bot.py", line 559, in _remove_module_references
    self.remove_cog(cogname)
  File "discord/ext/commands/bot.py", line 545, in remove_cog
    cog._eject(self)
  File "discord/ext/commands/cog.py", line 424, in _eject
    self.cog_unload()
  File "bot/cogs/watchchannels/watchchannel.py", line 335, in cog_unload
    self._consume_task.result()

Extension 'bot.cogs.watchchannels' failed to reload.

[MarkKoz]

Duplicate of #1008