Fix empty mailing lists

storage.lua

@@ -346,6 +346,9 @@ function mail.get_maillist_by_name(playername, listname)
 	local entry = mail.get_storage_entry(playername)
 	for _, list in ipairs(entry.lists) do
 		if list.name == listname then
+			if not list.players then
+				list.players = {}
+			end
 			return list
 		end
 	end
@@ -362,6 +365,9 @@ function mail.update_maillist(playername, list, old_list_name)
 		end
 	end
 	-- insert
+	if not list.players then
+		list.players = {}
+	end
 	table.insert(entry.lists, list)
 	mail.set_storage_entry(playername, entry)
 end