Issue 38128: IDLE undo calls get_saved() when set to None

Terry, I don't know if these exception reports are useful to you.  If not, feel free to close this.  I run IDLE in day long sessions and only see these tracebacks when I'm exiting, so I don't know the proximate trigger event.


Exception in Tkinter callback
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/tkinter/__init__.py", line 1883, in __call__
    return self.func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/multicall.py", line 176, in handler
    r = l[i](event)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/filelist.py", line 54, in close_all_callback
    reply = edit.close()
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/pyshell.py", line 1008, in close
    return EditorWindow.close(self)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/editor.py", line 1077, in close
    reply = self.maybesave()
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/outwin.py", line 94, in maybesave
    return 'yes' if self.get_saved() else 'no'
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/editor.py", line 1010, in get_saved
    return self.undo.get_saved()
AttributeError: 'NoneType' object has no attribute 'get_saved'

Here's one more:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/tkinter/__init__.py", line 1883, in __call__
    return self.func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/multicall.py", line 176, in handler
    r = l[i](event)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/filelist.py", line 54, in close_all_callback
    reply = edit.close()
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/editor.py", line 1079, in close
    self._close()
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/pyshell.py", line 312, in _close
    EditorWindow._close(self)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/editor.py", line 1083, in _close
    if self.io.filename:
AttributeError: 'NoneType' object has no attribute 'filename'