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>

src/saveload/afterload.cpp

@@ -3234,6 +3234,13 @@ bool AfterLoadGame()
 		_new_competitor_timeout.fired = _new_competitor_timeout.period == 0;
 	}
 
+	if (IsSavegameVersionBefore(SLV_NEWGRF_LAST_SERVICE)) {
+		/* Set service date provided to NewGRF. */
+		for (Vehicle *v : Vehicle::Iterate()) {
+			v->date_of_last_service_newgrf = v->date_of_last_service;
+		}
+	}
+
 	AfterLoadLabelMaps();
 	AfterLoadCompanyStats();
 	AfterLoadStoryBook();