branch 2.1-pgp-smime: exception, undefined sigfilename

[Kai Engert]

This bug report is specific to branch https://code.launchpad.net/~joostvb/mailman/2.1-pgp-smime

When receiving certain messages, python throws this exception:

Uncaught runner exception: local variable 'sigfilename' referenced before assignment
Traceback (most recent call last):
  File "/usr/local/mmcrypto/Mailman/Queue/Runner.py", line 119, in _oneloop
    self._onefile(msg, msgdata)
  File "/usr/local/mmcrypto/Mailman/Queue/Runner.py", line 190, in _onefile
    keepqueued = self._dispose(mlist, msg, msgdata)
  File "/usr/local/mmcrypto/Mailman/Queue/IncomingRunner.py", line 130, in _dispose
    more = self._dopipeline(mlist, msg, msgdata, pipeline)
  File "/usr/local/mmcrypto/Mailman/Queue/IncomingRunner.py", line 153, in _dopipeline
    sys.modules[modname].process(mlist, msg, msgdata)
  File "/usr/local/mmcrypto/Mailman/Handlers/Moderate.py", line 318, in process
    key_ids.extend(gh.verifyMessage(payload, signature))
  File "/usr/local/mmcrypto/Mailman/GPGUtils.py", line 374, in verifyMessage
    if sigfilename:
UnboundLocalError: local variable 'sigfilename' referenced before assignment

I'll propose a patch to avoid the exception.