Fix macro_set index out of range bug (#4972)

# About the pull request

![image](https://github.com/cmss13-devs/cmss13/assets/41448081/6ddb3b06-8e72-4b23-8b2a-14ea8a2315a1)

code/modules/keybindings/setup.dm

@@ -15,7 +15,7 @@
 	for(var/k in 1 to length(macro_set))
 		var/list/split_name = splittext(macro_set[k], ".")
 
-		if(findtext(split_name[2], "srvkeybinds-") == 1)
+		if((length(split_name) >= 2) && (findtext(split_name[2], "srvkeybinds-") == 1))
 			var/macro_name = "[split_name[1]].[split_name[2]]" // [3] is "command"
 			erase_output = "[erase_output];[macro_name].parent=null"
 	winset(src, null, erase_output)