Teleport Rail causes NullPointerException if not part of a rail network

[GsakuL]

If not properly set up with Station Markers / Signals, the Teleport Rail just straight up crashes the server. e.g. https://pastebin.com/PtzDPuyH In com.minemaarten.signals.block.BlockTeleportRail.getNeighboringTeleportRails the variable edge (line 175) will be null.

This could happen to new users. Or accidentally, if a cart gets pushed onto the rail, without care.