The `unload` method fails for watchchannels if the consume task hasn't started yet
The `unload_cog` method of the `WatchChannel` ABC has a small bug in it. If you try to reload or unload the cog while the message consumption task has not yet started, it will fail because the `bot._consume_task` attribute will still be assigned to `None`:

https://github.com/python-discord/bot/blob/cff9cabfee014e6207e156ee69e8b326ece55800/bot/cogs/watchchannels/watchchannel.py#L335-L339

This will lead to the following exception, which also prevents us from reloading the extensions that have cogs that derive from this ABC completely:

```py
Traceback (most recent call last):
  File "/home/sebastiaan/pydis/repositories/djangobot/bot/cogs/cogs.py", line 232, in reload_command
    self.bot.unload_extension(full_cog)
  File "/home/sebastiaan/.local/share/virtualenvs/djangobot-Py5o4YeS/lib/python3.7/site-packages/discord/ext/commands/bot.py", line 655, in unload_extension
    self._remove_module_references(lib.__name__)
  File "/home/sebastiaan/.local/share/virtualenvs/djangobot-Py5o4YeS/lib/python3.7/site-packages/discord/ext/commands/bot.py", line 534, in _remove_module_references
    self.remove_cog(cogname)
  File "/home/sebastiaan/.local/share/virtualenvs/djangobot-Py5o4YeS/lib/python3.7/site-packages/discord/ext/commands/bot.py", line 520, in remove_cog
    cog._eject(self)
  File "/home/sebastiaan/.local/share/virtualenvs/djangobot-Py5o4YeS/lib/python3.7/site-packages/discord/ext/commands/cog.py", line 414, in _eject
    self.cog_unload()
  File "/home/sebastiaan/pydis/repositories/djangobot/bot/cogs/watchchannels/watchchannel.py", line 338, in cog_unload
    if not self._consume_task.done():
AttributeError: 'NoneType' object has no attribute 'done'
```

So, we need to make sure that a `Task` was assigned in the first place, before trying to access the `done` method of it.
diff --git a/bot/cogs/watchchannels/watchchannel.py b/bot/cogs/watchchannels/watchchannel.py
index ce8014d6..760e012e 100644
--- a/bot/cogs/watchchannels/watchchannel.py
+++ b/bot/cogs/watchchannels/watchchannel.py
@@ -335,7 +335,7 @@ class WatchChannel(metaclass=CogABCMeta):
     def cog_unload(self) -> None:
         """Takes care of unloading the cog and canceling the consumption task."""
         self.log.trace(f"Unloading the cog")
-        if not self._consume_task.done():
+        if self._consume_task and not self._consume_task.done():
             self._consume_task.cancel()
             try:
                 self._consume_task.result()
['bot/cogs/watchchannels/watchchannel.py']