Fixed bug in be-handle-mail.Message.parse_comment() for emails w/o Message-id.

Fixed bug in be-handle-mail.Message.parse_comment() for emails w/o Message-id.

You used to get:

Uncaught exception:
'NoneType' object has no attribute 'decode'
  File "./be-handle-mail", line 857, in main
    m.run()
  File "./be-handle-mail", line 591, in run
    command.run()
  File "./be-handle-mail", line 244, in run
    manipulate_encodings=False)
  File "/tmp/be.email-bugs/interfaces/email/interactive/libbe/cmdutil.py", line 82, in execute
    ret = cmd.execute([a.decode(enc) for a in args],

A `print args' in Message.parse_comment() revealed
  [..., u'--alt-id', None,...]