Description of problem:

The choose-cd dialog fails to appear again after being dismissed with the Escape key.  It is necessary to quit and restart virt-manager in order to get the choose-cd dialog back again.

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

virt-manager.git/master and virt-manager-0.8.4-8 Debian package

Steps to Reproduce:
1. Start virt-manager and open the details for a virtual machine.
2. Select "IDE CDROM 1".
3. Click "Connect" to open the choose-cd dialog.
4. Press the Escape key (do not click cancel, this bug only affects the escape key binding).
5. Click "Connect" again.
  
Actual results:

The choose-cd dialog does not appear again when "Connect" is clicked.  The following backtrace is in the virt-manager log file:
[Sat, 19 Mar 2011 11:25:20 virt-manager 13033] DEBUG (engine:628) window counter incremented to 2
[Sat, 19 Mar 2011 11:26:23 virt-manager 13033] ERROR (virt-manager:173) Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/details.py", line 1185, in toggle_storage_media
    dialog.show()
  File "/usr/share/virt-manager/virtManager/choosecd.py", line 81, in show
    self.reset_state()
  File "/usr/share/virt-manager/virtManager/choosecd.py", line 86, in reset_state
    use_cdrom = (cd_path.get_active() > -1)
AttributeError: 'NoneType' object has no attribute 'get_active'
None

Expected results:

The choose-cd dialog should reappear when "Connect" is clicked after it was dismissed earlier by pressing the Escape key.