util.prosodyctl.check: Fix error where hostname can't be turned into A label Where gethostname or tohostname returns an invalid name, e.g. containing underscores or something, to_ascii would reject this and return nil, which triggers an error in the dns lookup. Reported by prova2 in the chat, for whom tohostname returned a long name containing underscores.

local set = require "util.set";

return {
	available = set.new{
		-- mod_bookmarks bundled
		"mod_bookmarks";

		"s2sout-pre-connect-event";
	};
};