QLineEdit: Disable standard key 'cut' when there is no selection.

(cherry-picked from qtbase/0aa84a619ea0a7c85a1ed48ed28817d4c7e40b33)
Task-number: QTBUG-40477
Change-Id: I48aa7ecc4ee8a8e4e9feaf9b6cba5109d2d1f725
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>