QAbstractItemView: Fix isPersistentEditorOpen for non-persistent editors
isPersistentEditorOpen() returned true if an editor widget existed for the given index, even when it was not opened as a persistent editor.
Update the implementation to check both that the editor widget exists and that it is listed in the persistent editor set.
Pick-to: 6.10 6.9 Fixes: QTBUG-72333 Change-Id: I380fb51a4e357b5497fb1462e4dcd40c7ead4e13 Reviewed-by: David Faure david.faure@kdab.com