title: Find out if WPF windows has been already loaded (Loaded event fired already)
body: <p>Is it possible to find out whether WPF Window is loaded?
  I have a method which accepts a window and hooks 'Loaded' event to it.
  If window is already loaded, the event will not fire.
  Is it possible to know this when accepting the argument?</p>
  
  <p>Thank you.</p>