Delay vehicle cache init to after map upgrades in load

Split AfterLoadVehicles into two functions.
Vehicle cache init and other functionality requiring an upgraded and
valid map is now performed later in the load process.

Re-order load update for SLV_139, it is no longer required to be
performed before the first phase of vehicle updates

src/sl/saveload_internal.h

@@ -25,7 +25,8 @@ void MoveBuoysToWaypoints();
 void MoveWaypointsToBaseStations();
 SaveLoadTable GetBaseStationDescription();
 
-void AfterLoadVehicles(bool part_of_load);
+void AfterLoadVehiclesPhase1(bool part_of_load);
+void AfterLoadVehiclesPhase2(bool part_of_load);
 void AfterLoadVehiclesRemoveAnyFoundInvalid();
 void AfterLoadEngines();
 void FixupTrainLengths();