Don't crash if a window no longer exists.

Tools/idle/WindowList.py

@@ -19,7 +19,10 @@ class WindowList:
         list = []
         for key in self.dict.keys():
             window = self.dict[key]
+            try:
                 title = window.get_title()
+            except TclError:
+                continue
             list.append((title, window))
         list.sort()
         for title, window in list: