Fix feedforward acceleration setpoints for fixedwing offboard position

This commit fixes feedforward acceleration setpoints for fixedwing offboard position control.

Previously when acceleration feedforward inputs were sent, negative curvature accelerations were not being computed properly

src/modules/fw_pos_control_l1/FixedwingPositionControl.cpp

@@ -2161,10 +2161,13 @@ FixedwingPositionControl::Run()
 					if (PX4_ISFINITE(trajectory_setpoint.acceleration[0]) && PX4_ISFINITE(trajectory_setpoint.acceleration[1])
 					    && PX4_ISFINITE(trajectory_setpoint.acceleration[2])) {
 						Vector2f velocity_sp_2d(trajectory_setpoint.velocity[0], trajectory_setpoint.velocity[1]);
+						Vector2f normalized_velocity_sp_2d = velocity_sp_2d.normalized();
 						Vector2f acceleration_sp_2d(trajectory_setpoint.acceleration[0], trajectory_setpoint.acceleration[1]);
-						Vector2f acceleration_normal = acceleration_sp_2d - acceleration_sp_2d.dot(velocity_sp_2d) *
-									       velocity_sp_2d.normalized();
-						_pos_sp_triplet.current.loiter_radius = velocity_sp_2d.norm() * velocity_sp_2d.norm() / acceleration_normal.norm();
+						Vector2f acceleration_normal = acceleration_sp_2d - acceleration_sp_2d.dot(normalized_velocity_sp_2d) *
+									       normalized_velocity_sp_2d;
+						float direction = -normalized_velocity_sp_2d.cross(acceleration_normal.normalized());
+						_pos_sp_triplet.current.loiter_radius = direction * velocity_sp_2d.norm() * velocity_sp_2d.norm() /
+											acceleration_normal.norm();
 
 					} else {
 						_pos_sp_triplet.current.loiter_radius = NAN;