Fix: only count distance traveled in vehicles for cargo payment (#11283)

No longer you can utilize the free (and instant) labour of station
workers, transporting your cargo from one part of the station to
the other. No more!

Based on patch by dP.

src/saveload/cargopacket_sl.cpp

@@ -76,6 +76,42 @@
 	if (IsSavegameVersionBefore(SLV_181)) {
 		for (Vehicle *v : Vehicle::Iterate()) v->cargo.KeepAll();
 	}
+
+	/* Before this version, we didn't track how far cargo actually traveled in vehicles. Make best-effort estimates of this. */
+	if (IsSavegameVersionBefore(SLV_CARGO_TRAVELLED)) {
+		/* Update the cargo-traveled in stations as if they arrived from the source tile. */
+		for (Station *st : Station::Iterate()) {
+			for (size_t i = 0; i < NUM_CARGO; i++) {
+				GoodsEntry *ge = &st->goods[i];
+				for (auto it = ge->cargo.Packets()->begin(); it != ge->cargo.Packets()->end(); it++) {
+					for (CargoPacket *cp : it->second) {
+						if (cp->source_xy != INVALID_TILE && cp->source_xy != st->xy) {
+							cp->travelled.x = TileX(cp->source_xy) - TileX(st->xy);
+							cp->travelled.y = TileY(cp->source_xy) - TileY(st->xy);
+						}
+					}
+				}
+			}
+		}
+
+		/* Update the cargo-traveled in vehicles as if they were loaded at the source tile. */
+		for (Vehicle *v : Vehicle::Iterate()) {
+			for (auto it = v->cargo.Packets()->begin(); it != v->cargo.Packets()->end(); it++) {
+				if ((*it)->source_xy != INVALID_TILE) {
+					(*it)->UpdateLoadingTile((*it)->source_xy);
+				}
+			}
+		}
+	}
+
+#ifdef WITH_ASSERT
+	/* in_vehicle is a NOSAVE; it tells if cargo is in a vehicle or not. Restore the value in here. */
+	for (Vehicle *v : Vehicle::Iterate()) {
+		for (auto it = v->cargo.Packets()->begin(); it != v->cargo.Packets()->end(); it++) {
+			(*it)->in_vehicle = true;
+		}
+	}
+#endif /* WITH_ASSERT */
 }
 
 /**
@@ -97,6 +133,8 @@ SaveLoadTable GetCargoPacketDesc()
 		SLE_VAR(CargoPacket, feeder_share,    SLE_INT64),
 		SLE_CONDVAR(CargoPacket, source_type,     SLE_UINT8,  SLV_125, SL_MAX_VERSION),
 		SLE_CONDVAR(CargoPacket, source_id,       SLE_UINT16, SLV_125, SL_MAX_VERSION),
+		SLE_CONDVAR(CargoPacket, travelled.x, SLE_INT16, SLV_CARGO_TRAVELLED, SL_MAX_VERSION),
+		SLE_CONDVAR(CargoPacket, travelled.y, SLE_INT16, SLV_CARGO_TRAVELLED, SL_MAX_VERSION),
 	};
 	return _cargopacket_desc;
 }