Valentin Lorentz 32d8d141ad Make irc.error do nothing is no string is given as argument.
Fixes c1d3bad64feca2529e29473f0ed8c622ad1937b1, 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
```
2020-01-18 11:04:54 +01:00
..
2018-10-06 08:13:10 +02:00
2015-08-11 16:50:23 +02:00
2017-09-19 00:34:25 +02:00
2019-10-10 17:27:34 +02:00
2019-11-24 12:47:03 +01:00
2019-01-06 18:08:15 +01:00
2015-08-11 16:50:23 +02:00