FlightTaskManualAltitude: call FlightTaskManualStabilized::_updateHeadingSetpoints() directly

Instead of calling _updateSetpoints(), that also sets the thrust setpoint,
which is then overwritten again.

src/lib/FlightTasks/tasks/ManualAltitude/FlightTaskManualAltitude.cpp

@@ -251,9 +251,7 @@ void FlightTaskManualAltitude::_respectMaxAltitude()
 
 void FlightTaskManualAltitude::_updateSetpoints()
 {
-	FlightTaskManualStabilized::_updateSetpoints(); // get yaw and thrust setpoints
-
-	_thrust_setpoint *= NAN; // Don't need thrust setpoint from Stabilized mode.
+	FlightTaskManualStabilized::_updateHeadingSetpoints(); // get yaw setpoint
 
 	// Thrust in xy are extracted directly from stick inputs. A magnitude of
 	// 1 means that maximum thrust along xy is demanded. A magnitude of 0 means no
@@ -269,6 +267,7 @@ void FlightTaskManualAltitude::_updateSetpoints()
 
 	_thrust_setpoint(0) = sp(0);
 	_thrust_setpoint(1) = sp(1);
+	_thrust_setpoint(2) = NAN;
 
 	_updateAltitudeLock();
 }