Refactored some of the navlist code and removed the built in "fail to find"

Refactored some of the navlist code and removed the built in "fail to find"
if the station is too far away.  Instead, simply return the closest station.
All the code that searches navaids does it's own range checking anyway.
This will make the navlist query functions a bit more useful for other
types of functionality where you may need to lookup a station without
consideration of range (i.e. presetting your position relative to a navaid.)