While feacaf8714 changed the API to allow
using any wxWindow (and not only a window of a wxControl-derived class)
as the associated window of the grid editor, actually doing resulted in
an immediate crash due to dereferencing a null pointer in wxGrid code
which still expected to have a wxControl.
Fix this by replacing all calls to wxGridCellEditor::GetControl() inside
wxGrid with wxGridCellEditor::GetWindow(), to ensure that a non-null
editor window is used even in this case.
Closes https://github.com/wxWidgets/wxWidgets/pull/1509
1bce1a1d4c