Fix #10334: Store separate newgrf-safe version of date_of_last_service. (#11124)

This value is not changed when the date cheat is used, which caused issues with changing properties based on service date.

Co-authored-by: Peter Nelson <peter1138@openttd.org>
(cherry picked from commit 9a602ff304)

src/articulated_vehicles.cpp

@@ -475,6 +475,7 @@ void AddArticulatedParts(Vehicle *first)
 		/* get common values from first engine */
 		v->owner = first->owner;
 		v->date_of_last_service = first->date_of_last_service;
+		v->date_of_last_service_newgrf = first->date_of_last_service_newgrf;
 		v->build_year = first->build_year;
 
 		v->cargo_subtype = 0;