Fix: don't allow cloning vehicles if cloning orders is failing (#8515)

Before this fix, any failing clone order was silently ignored
and you as user would never know till you checked the order list.
Evil.

src/vehicle_cmd.cpp

@@ -978,7 +978,12 @@ CommandCost CmdCloneVehicle(TileIndex tile, DoCommandFlag flags, uint32 p1, uint
 		 * the vehicle refitted before doing this, otherwise the moved
 		 * cargo types might not match (passenger vs non-passenger)
 		 */
-		DoCommand(0, w_front->index | (p2 & 1 ? CO_SHARE : CO_COPY) << 30, v_front->index, flags, CMD_CLONE_ORDER);
+		CommandCost result = DoCommand(0, w_front->index | (p2 & 1 ? CO_SHARE : CO_COPY) << 30, v_front->index, flags, CMD_CLONE_ORDER);
+		if (result.Failed()) {
+			/* The vehicle has already been bought, so now it must be sold again. */
+			DoCommand(w_front->tile, w_front->index | 1 << 20, 0, flags, GetCmdSellVeh(w_front));
+			return result;
+		}
 
 		/* Now clone the vehicle's name, if it has one. */
 		if (!v_front->name.empty()) CloneVehicleName(v_front, w_front);