Bugfix in pure python aui: Early return from method if underlying C++ object has been destroyed

[jmoraleda]

When the application is in the process of changing the aui layout programmatically (e.g. by loading a perspective) it is possible to click on a notebook pane that is in the process of being destroyed. This results in the error:

Traceback (most recent call last):
  File "/usr/local/lib/python3.11/dist-packages/wx/core.py", line 2346, in Notify
    self.notify()
  File "/usr/local/lib/python3.11/dist-packages/wx/core.py", line 3552, in Notify
    self.result = self.callable(*self.args, **self.kwargs)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/wx/lib/agw/aui/auibook.py", line 2504, in ShowTooltip
    wnd = self.GetPointedToTab()
          ^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/wx/lib/agw/aui/auibook.py", line 2462, in GetPointedToTab
    client_pt = self.ScreenToClient(screen_pt)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: wrapped C/C++ object of type AuiTabCtrl has been deleted

This PR fixes the bug in the conventional way: By testing for self truthiness. and returning early without invoking any member methods if it is False.

[jmoraleda]

I think we should wait before merging this PR. As I do intensive testing I am finding that the pure python AUI seems to have several race conditions leading to similar errors. I am going to try to produce a comprehensive solution and I will update this PR when I have something that I think is stable.

These are two of the errors, but there are more

2023-11-08 19:21:00 ERROR [wx.lib.agw.aui.framemanager]: An unexpected error occurred in wx.lib.agw.aui.framemanager.
Traceback (most recent call last):
  File "C:\Program Files\Prog 1.0\WPy64-31120b3\python-3.11.2.amd64\Lib\site-packages\wx\lib\agw\aui\framemanager.py", line 8967, in OnMotion
    self.OnMotion_Resize(event)
  File "C:\Program Files\Prog 1.0\WPy64-31120b3\python-3.11.2.amd64\Lib\site-packages\wx\lib\agw\aui\framemanager.py", line 9180, in OnMotion_Resize
    self._currentDragItem = self._uiparts.index(self._action_part)
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: None is not in list

RuntimeError: wrapped C/C++ object of type AuiNotebook has been deleted
2023-11-08 10:43:28 ERROR [wx.lib.agw.aui.framemanager]: An unexpected error occurred in wx.lib.agw.aui.framemanager.
Traceback (most recent call last):
  File "C:\Program Files\Prog 1.0\WPy64-31120b3\python-3.11.2.amd64\Lib\site-packages\wx\lib\agw\aui\framemanager.py", line 8443, in OnRender
    art.DrawCaption(dc, self._frame, part.pane.caption, part.rect, part.pane)
  File "C:\Program Files\Prog 1.0\WPy64-31120b3\python-3.11.2.amd64\Lib\site-packages\wx\lib\agw\aui\dockart.py", line 593, in DrawCaption
    btns = pane.CountButtons()
           ^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Prog 1.0\WPy64-31120b3\python-3.11.2.amd64\Lib\site-packages\wx\lib\agw\aui\framemanager.py", line 1715, in CountButtons
    if isinstance(wx.GetTopLevelParent(self.window), AuiFloatingFrame):
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In retrospect, I realize I should have just opened an issue rather than a PR. But I am cautiously optimistic that I'll be able to turn this into a bona fide PR.

[jmoraleda]

I am going to close this PR until I have done sufficient testing an the patch set to believe that the assorted "wrapped C/C++ object has been deleted" and related race conditions have been eradicated, or at least are very significantly reduced from the current level.