Multiserver: warn about missing items_handling

MultiServer.py

@@ -1353,6 +1353,8 @@ async def process_client_cmd(ctx: Context, client: Client, args: dict):
                 client.no_items = False
                 client.remote_items = slot in ctx.remote_items
                 client.remote_start_inventory = slot in ctx.remote_start_inventory
+                ctx.send_msgs([{"cmd": "Print", "text": "Warning: Client is not sending items_handling flags, "
+                                                        "which will not be supported in the future."}])
             else:
                 try:
                     client.items_handling = args['items_handling']