don't overwrite waypoints while setting

init.lua

@@ -327,6 +327,13 @@ minetest.register_chatcommand('wp_set', {
     func = safe(function(param)
         waypoints = load_waypoints()
         local point = minetest.localplayer:get_pos()
+        if waypoints[param] then
+	   minetest.display_chat_message(
+		 ('waypoint "%s" not saved: already set'):format(param)
+				      )
+	   return
+	end
+	   
         waypoints[param] = point
         mod_storage:set_string('waypoints', minetest.serialize(waypoints))