Fix unreserving through a green PBS signal not setting the state to red.

This also had the side effect of failed reservation attempts through
a reserve-through signal leaving the signal erroneously set to green.

src/pathfinder/yapf/yapf_rail.cpp

@@ -119,7 +119,7 @@ private:
 				tile = TILE_ADD(tile, diff);
 			}
 		} else if (tile != m_res_fail_tile || td != m_res_fail_td) {
-			UnreserveRailTrack(tile, TrackdirToTrack(td));
+			UnreserveRailTrackdir(tile, td);
 		}
 		return (tile != m_res_dest || td != m_res_dest_td) && (tile != m_res_fail_tile || td != m_res_fail_td);
 	}

src/pbs.cpp

@@ -154,6 +154,20 @@ bool TryReserveRailTrack(TileIndex tile, Track t, bool trigger_stations)
 	return false;
 }
 
+/**
+ * Lift the reservation of a specific trackdir on a tile
+ * This also sets PBS signals to red if unreserving through the facing track direction
+ * @param tile the tile
+ * @param t the track
+ */
+void UnreserveRailTrackdir(TileIndex tile, Trackdir td)
+{
+	if (HasPbsSignalOnTrackdir(tile, td)) {
+		SetSignalStateByTrackdir(tile, td, SIGNAL_STATE_RED);
+	}
+	UnreserveRailTrack(tile, TrackdirToTrack(td));
+}
+
 /**
  * Lift the reservation of a specific track on a tile
  * @param tile the tile

src/pbs.h

@@ -24,6 +24,7 @@ void SetRailStationPlatformReservation(TileIndex start, DiagDirection dir, bool
 bool TryReserveRailTrack(TileIndex tile, Track t, bool trigger_stations = true);
 bool TryReserveRailTrackdir(TileIndex tile, Trackdir td, bool trigger_stations = true);
 void UnreserveRailTrack(TileIndex tile, Track t);
+void UnreserveRailTrackdir(TileIndex tile, Trackdir td);
 
 /** This struct contains information about the end of a reserved path. */
 struct PBSTileInfo {

src/train_cmd.cpp

@@ -2415,7 +2415,7 @@ static PBSTileInfo ExtendTrainReservation(const Train *v, const PBSTileInfo &ori
 		tile = ft.m_new_tile;
 		cur_td = FindFirstTrackdir(ft.m_new_td_bits);
 
-		UnreserveRailTrack(tile, TrackdirToTrack(cur_td));
+		UnreserveRailTrackdir(tile, cur_td);
 	}
 
 	/* Path invalid. */