Fixes c1d3bad64f, which crashed with:
```
ERROR 2020-01-18T01:34:07 Uncaught exception in NickAuth._callCommand:
Traceback (most recent call last):
File "/usr/local/lib/python3.7/dist-packages/supybot/callbacks.py", line 1337, in _callCommand
irc.errorNoCapability(cap)
File "/usr/local/lib/python3.7/dist-packages/supybot/callbacks.py", line 544, in errorNoCapability
raise Error()
supybot.callbacks.Error
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/lib/python3.7/dist-packages/supybot/log.py", line 368, in m
return f(self, *args, **kwargs)
File "/usr/local/lib/python3.7/dist-packages/supybot/callbacks.py", line 1359, in _callCommand
irc.error(str(e))
File "/usr/local/lib/python3.7/dist-packages/supybot/callbacks.py", line 1065, in error
raise ArgumentError
supybot.callbacks.ArgumentError
```
32d8d141ad