Querying non-existent repo causes exception

[Max Rabkin]

<Taejo> tibid: last commit to roflmao
<tibid> Taejo: I'm not feeling too well
<Taejo> tibid: last traceback
<tibid> File "/home/stefanor/bzr/ibid/stefanor/tibid/ibid/core.py", line 33, in _process
<tibid> processor.process(event)
<tibid> File "/home/stefanor/bzr/ibid/stefanor/tibid/ibid/plugins/__init__.py", line 148, in process
<tibid> method(event, *args)
<tibid> File "/home/stefanor/bzr/ibid/stefanor/tibid/ibid/plugins/bzr.py", line 118, in commit
<tibid> for commit in commits:
<tibid> TypeError: 'NoneType' object is not iterable