Enable signals on bridges/tunnels to work with PBS.

src/pathfinder/npf/npf.cpp

@@ -936,6 +936,10 @@ static void NPFFollowTrack(AyStar *aystar, OpenListNode *current)
 				break;
 			}
 		}
+		if (IsTileType(dst_tile, MP_TUNNELBRIDGE) && IsTunnelBridgeExit(dst_tile) && DiagDirToDiagTrackdir(GetTunnelBridgeDirection(dst_tile)) == dst_trackdir) {
+			/* Entering a signalled bridge/tunnel from the wrong side, equivalent to encountering a one-way signal from the wrong side */
+			break;
+		}
 		{
 			/* We've found ourselves a neighbour :-) */
 			AyStarNode *neighbour = &aystar->neighbours[i];