ensure attitude setpoint initialization before arming

- On initialization _v_att_sp got filled with zeros
  leaving invalid quaternions
- While not armed mc_pos_control did not publish any
  attitude setpoint which makes no sense
- The attitude control just uses the data in _v_att_sp
  if it was (ever) updated or not

src/modules/mc_att_control/mc_att_control_main.cpp

@@ -389,6 +389,10 @@ _loop_update_rate_hz(initial_update_rate_hz)
 
 	_vehicle_status.is_rotary_wing = true;
 
+	/* initialize quaternions in messages to be valid */
+	_v_att.q[0] = 1.f;
+	_v_att_sp.q_d[0] = 1.f;
+
 	_params.rate_p.zero();
 	_params.rate_i.zero();
 	_params.rate_int_lim.zero();

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -3234,13 +3234,11 @@ MulticopterPositionControl::task_main()
 		 * in this case the attitude setpoint is published by the mavlink app.
 		 * - if the vehicle is a VTOL and it's just doing a transition (the VTOL attitude control module will generate
 		 * attitude setpoints for the transition).
-		 * - if not armed
 		 */
-		if (_control_mode.flag_armed &&
-		    (!(_control_mode.flag_control_offboard_enabled &&
-		       !(_control_mode.flag_control_position_enabled ||
-			 _control_mode.flag_control_velocity_enabled ||
-			 _control_mode.flag_control_acceleration_enabled)))) {
+		if (!(_control_mode.flag_control_offboard_enabled &&
+		      !(_control_mode.flag_control_position_enabled ||
+			_control_mode.flag_control_velocity_enabled ||
+			_control_mode.flag_control_acceleration_enabled))) {
 
 			if (_att_sp_pub != nullptr) {
 				orb_publish(_attitude_setpoint_id, _att_sp_pub, &_att_sp);