navigator: fix loiter_time for FW missions

src/modules/navigator/mission_block.cpp

@@ -224,7 +224,10 @@ MissionBlock::is_mission_item_reached()
 			 * Therefore the item is marked as reached once the system reaches the loiter
 			 * radius (+ some margin). Time inside and turn count is handled elsewhere.
 			 */
-			if (dist >= 0.0f && dist <= _navigator->get_acceptance_radius(fabsf(_mission_item.loiter_radius) * 1.2f)
+			float radius = (fabsf(_mission_item.loiter_radius) > NAV_EPSILON_POSITION) ? fabsf(_mission_item.loiter_radius) :
+				       _navigator->get_loiter_radius();
+
+			if (dist >= 0.0f && dist <= _navigator->get_acceptance_radius(fabsf(radius) * 1.2f)
 			    && dist_z <= _navigator->get_altitude_acceptance_radius()) {
 
 				_waypoint_position_reached = true;