Description of problem:
Yumex crashes.

Version-Release number of selected component (if applicable):
0.99.16

How reproducible:
100% on my machine.

Steps to Reproduce:
1. Open Yumex (no refresh on start) and do nothing (especially not refresh the
repo list).
2. Open the preferences dialog and then hit "cancel" without changig anything.
3. Yumex crashes
  
Actual results:
I got this Traceback

Component: yumex
Version: 0.99.16
Summary: TB3c1b0dfc yumexmain.py:595:doPref:AttributeError: 'NoneType' object
has no attribute 'yumexconf'

Traceback (most recent call last):
  File "/usr/share/yumex/yumexmain.py", line 209, in on_EditPreferences
    self.doPref()
  File "/usr/share/yumex/yumexmain.py", line 595, in doPref
    self.yumexbase.yumexconf = self.settings
AttributeError: 'NoneType' object has no attribute 'yumexconf'

Local variables in innermost frame:
self: <__main__.YumexMainApplication instance at 0xb79e926c>

Expected results:
At least I would expect it not to crash ;).

Additional info:
Mail me if you got additional questions.