if you select a system to navigat to, the orange line will become dashed at the system where the next jump will exceed your fuel capacity. so you should check if that last system has a station to refuel or - if you have a fuel scoop with you - you end up in a system with one of the following start types: O, B, A, F, G, K, M
In any other case, you should reroute your path or you mights strand in that system... what can you do if you do so btw? suicide?