positionControl: add check on sign before sqrtf

src/modules/mc_pos_control/PositionControl/PositionControl.cpp

@@ -164,7 +164,12 @@ void PositionControl::_velocityControl(const float dt)
 	// Get allowed horizontal thrust after prioritizing vertical control
 	const float thrust_max_squared = _lim_thr_max * _lim_thr_max;
 	const float thrust_z_squared = _thr_sp(2) * _thr_sp(2);
-	float thrust_max_xy = sqrtf(thrust_max_squared - thrust_z_squared);
+	const float thrust_max_xy_squared = thrust_max_squared - thrust_z_squared;
+	float thrust_max_xy = 0;
+
+	if (thrust_max_xy_squared > 0) {
+		thrust_max_xy = sqrtf(thrust_max_xy_squared);
+	}
 
 	// Saturate thrust in horizontal direction
 	const Vector2f thrust_sp_xy(_thr_sp);