openid: Fix notice about unititialized variable.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3027 44740490-163a-0410-bde0-09ae8108e29a

modules/openid/www/consumer.php

@@ -13,6 +13,7 @@ if ($authSource === NULL) {
 	throw new SimpleSAML_Error_BadRequest('Invalid AuthId \'' . $sourceId . '\' - not found.');
 }
 
+$error = NULL;
 try {
 	if (!empty($_GET['openid_url'])) {
 		$authSource->doAuth($state, (string)$_GET['openid_url']);