examples: set_attitude_target: avoid use of None in to_quaternion
examples: set_attitude_target: avoid use of None in to_quaternion

dronekit/dronekit-python,hamishwillee/dronekit-python,dronekit/dronekit-python,diydrones/dronekit-python,diydrones/dronekit-python,hamishwillee/dronekit-python