Fix #11307: Incorrect GroupStatistics after selling leading wagon

When this results in a countable consist

src/train_cmd.cpp

@@ -2334,18 +2334,20 @@ CommandCost CmdSellRailWagon(DoCommandFlag flags, Vehicle *t, uint16 data, uint3
 		/* First normalise the sub types of the chain. */
 		NormaliseSubtypes(new_head);
 
-		if (v == first && v->IsEngine() && !sell_chain && new_head != nullptr && new_head->IsFrontEngine()) {
-			/* We are selling the front engine. In this case we want to
-			 * 'give' the order, unit number and such to the new head. */
-			new_head->orders = first->orders;
-			new_head->AddToShared(first);
-			DeleteVehicleOrders(first);
-
-			/* Copy other important data from the front engine */
-			new_head->CopyVehicleConfigAndStatistics(first);
-			new_head->speed_restriction = first->speed_restriction;
-			SB(Train::From(new_head)->flags, VRF_SPEED_ADAPTATION_EXEMPT, 1, GB(Train::From(first)->flags, VRF_SPEED_ADAPTATION_EXEMPT, 1));
-			GroupStatistics::CountVehicle(new_head, 1); // after copying over the profit
+		if (v == first && !sell_chain && new_head != nullptr && new_head->IsFrontEngine()) {
+			if (v->IsEngine()) {
+				/* We are selling the front engine. In this case we want to
+				 * 'give' the order, unit number and such to the new head. */
+				new_head->orders = first->orders;
+				new_head->AddToShared(first);
+				DeleteVehicleOrders(first);
+
+				/* Copy other important data from the front engine */
+				new_head->CopyVehicleConfigAndStatistics(first);
+				new_head->speed_restriction = first->speed_restriction;
+				SB(Train::From(new_head)->flags, VRF_SPEED_ADAPTATION_EXEMPT, 1, GB(Train::From(first)->flags, VRF_SPEED_ADAPTATION_EXEMPT, 1));
+			}
+			GroupStatistics::CountVehicle(new_head, 1); // after copying over the profit, if required
 		} else if (v->IsPrimaryVehicle() && data & (MAKE_ORDER_BACKUP_FLAG >> 20)) {
 			OrderBackup::Backup(v, user);
 		}