If a VM changes state while the details window is open, we attempt to repopulate the migrate connection menu. However, the population function erroneously depends on whatever is selected in the main manager view, which can cause issues like below:

2009-11-12 17:29:56,383 DEBUG    Uncaught Error: Error bringing up domain details: 'NoneType' object has no attribute 'get_driver' : Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/engine.py", line 272, in show_details
    details = vmmDetails(self.get_config(), con.get_vm(uuid), self)
  File "/usr/share/virt-manager/virtManager/details.py", line 329, in __init__
    self.update_widget_states(self.vm, self.vm.status())
  File "/usr/share/virt-manager/virtManager/details.py", line 739, in update_widget_states
    self.set_migrate_menu()
  File "/usr/share/virt-manager/virtManager/details.py", line 686, in set_migrate_menu
    self.engine.populate_migrate_menu(menu, self.control_vm_migrate)
  File "/usr/share/virt-manager/virtManager/engine.py", line 583, in populate_migrate_menu
    conns = self.get_available_migrate_hostnames()
  File "/usr/share/virt-manager/virtManager/engine.py", line 606, in get_available_migrate_hostnames
    driver = self.windowManager.current_connection().get_driver()
AttributeError: 'NoneType' object has no attribute 'get_driver'