This hopefully helps with a crash on Windows which happens from time to time
during some multi-window tabs.feature tests:
Traceback (most recent call last):
File "...\mainwindow\mainwindow.py", line 446, in closeEvent
self._do_close()
File "...\mainwindow\mainwindow.py", line 405, in _do_close
objreg.get('session-manager').save_last_window_session()
File "...\misc\sessions.py", line 247, in save_last_window_session
self._last_window_session = self._save_all()
File "...\misc\sessions.py", line 183, in _save_all
win_data['geometry'] = bytes(main_window.saveGeometry())
RuntimeError: wrapped C/C++ object of type MainWindow has been deleted