add error message

Author: cloudwu

src/lualib/layout.lua

@@ -128,7 +128,7 @@ do
 	function layout.load(filename_or_list, scripts)
 		local list
 		if type(filename_or_list) == "string" then
-			list = datalist.parse_list(file.load(filename_or_list))
+			list = datalist.parse_list(file.load(filename_or_list) or error ("Can't load " .. filename_or_list))
 		else
 			list = filename_or_list
 		end