Undo causes File widget to fail

[ajdapretnar]

Unfortunately, I've no idea what exactly happened. I've had a workflow, where I undid several steps (Cmd+Z). This included removing the File widget from the canvas. Then, I manually added File back, which triggered the error. I cannot reproduce it with simple steps.
Reporting just in case.

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QLayout: Attempting to add QLayout "" to ErrorReporting "", which already has a layout
QLayout: Attempting to add QLayout "" to ErrorReporting "", which already has a layout
-------------------------- AttributeError Exception ---------------------------
Traceback (most recent call last):
  File "/Users/ajda/orange/orange-canvas-core/orangecanvas/application/canvasmain.py", line 1635, in save_swp
    self.save_swp_to(swpname)
  File "/Users/ajda/orange/orange-canvas-core/orangecanvas/application/canvasmain.py", line 1645, in save_swp_to
    undoDiff = [UndoCommand.from_QUndoCommand(undoStack.command(i))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ajda/orange/orange-canvas-core/orangecanvas/application/canvasmain.py", line 1645, in <listcomp>
    undoDiff = [UndoCommand.from_QUndoCommand(undoStack.command(i))
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ajda/orange/orange-canvas-core/orangecanvas/document/commands.py", line 73, in from_QUndoCommand
    qc.__parent = parent
    ^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute '_UndoCommand__parent'
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