Fixed navradio when shutting down/restarting nav receiver.

Fixed navradio when shutting down/restarting nav receiver.
"nav-loc" and "has_gs" properties were not updated when nav receiver was rebooted.

Shutting down the nav receiver clears all nav outputs (including "nav-loc" and "has_gs").
=> When nav receiver is powered again, all outputs must be updated.
=> "nav-loc" and "has_gs" are only updated when active nav station changes.
=> old nav station must be cleared on shutdown to enforce update on nav reboot...