mc_pos_control: don't divide by zero

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -1599,7 +1599,7 @@ void MulticopterPositionControl::control_auto(float dt)
 						}
 
 						/* compute velocity at transition where vehicle switches from acceleration to deceleration */
-						if ((target_threshold_xy - acceptance_radius) < SIGMA_NORM) {
+						if ((target_threshold_tmp - acceptance_radius) < SIGMA_NORM) {
 							final_cruise_speed = vel_close;
 
 						} else {
@@ -1648,10 +1648,16 @@ void MulticopterPositionControl::control_auto(float dt)
 						if (vec_closest_to_current.length() < _nav_rad.get()) {
 							vel_sp_along_track = vel_close;
 
+						} else {
+
+							if (target_threshold_xy - _nav_rad.get() < SIGMA_NORM) {
+								vel_sp_along_track = vel_close;
+
 							} else {
 								float slope = (get_cruising_speed_xy() - vel_close) / (target_threshold_xy - _nav_rad.get()) ;
 								vel_sp_along_track = slope  * (vec_closest_to_current.length() - _nav_rad.get()) + vel_close;
 							}
+						}
 
 						/* since we want to slow down take over previous velocity setpoint along track if it was lower */
 						if ((vel_sp_along_track_prev < vel_sp_along_track) && (vel_sp_along_track * vel_sp_along_track_prev > 0.0f)) {