Fix warning message while tyying to print dn() not defined yet

--- ./lib/Net/LDAP/Config.pm	2006-05-28 09:20:25 +0400
+++ ./lib/Net/LDAP/Config.pm	2006-05-28 09:23:35 +0400
@@ -257,7 +257,7 @@
 		$config->dn($config->uid());
 	}
 
-	print $config->dn(), "\n";
+	print $config->dn(), "\n" if ($config->dn());
 
 	# this tells whether they are piping to us or have an interactive session
 	if (-t STDIN) {