Rover can end up outside the fence without the user doing anything particularly bad:

• create a polygon fence
• set LOIT_RADIUS to 10m
• place a waypoint with a 60s delay closer than 10m to the fence boundary

When the rover loiters at the waypoint it may stray outside the fence, RTL will trigger but the vehicle will not be able to return

To resolve this we should enhance Dijkstras so that it handles the case where the vehicle starts outside the fence