mission_block: explicitly (re)set the acceptance radius to default for takeoff items

otherwise a previously adjusted or uninitialized radius from the last flight
can cause problems during the new takeoff

src/modules/navigator/mission_block.cpp

@@ -821,6 +821,7 @@ MissionBlock::set_takeoff_item(struct mission_item_s *item, float abs_altitude)
 	item->altitude = abs_altitude;
 	item->altitude_is_relative = false;
 
+	item->acceptance_radius = _navigator->get_acceptance_radius();
 	item->loiter_radius = _navigator->get_loiter_radius();
 	item->autocontinue = false;
 	item->origin = ORIGIN_ONBOARD;