Fixed a small bug with atcommand addwarp

* The function that creates the warp was using the wrong Y area argument.
Thanks to @mrjnumber1!

src/map/npc.c

@@ -2464,7 +2464,7 @@ struct npc_data* npc_add_warp(char* name, short from_mapid, short from_x, short
 	nd->u.warp.x = to_x;
 	nd->u.warp.y = to_y;
 	nd->u.warp.xs = xs;
-	nd->u.warp.ys = xs;
+	nd->u.warp.ys = ys;
 	nd->bl.type = BL_NPC;
 	nd->subtype = NPCTYPE_WARP;
 	nd->trigger_on_hidden = false;