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/saveload/afterload.cpp

@@ -4222,6 +4222,13 @@ bool AfterLoadGame()
 		GenerateSavegameId();
 	}
 
+	if (IsSavegameVersionBefore(SLV_NEWGRF_LAST_SERVICE) && SlXvIsFeatureMissing(XSLFI_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;
+		}
+	}
+
 	InitializeRoadGUI();
 
 	/* This needs to be done after conversion. */