Prevent notice "Undefined variable: struct" in mt_getRecentPostTitles when posts exist, but none of them are editable. Fixes #20393.

git-svn-id: https://develop.svn.wordpress.org/trunk@20403 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/class-wp-xmlrpc-server.php

@@ -4502,6 +4502,8 @@ class wp_xmlrpc_server extends IXR_Server {
 			return $this->error;
 		}
 
+		$struct = array();
+
 		foreach ($posts_list as $entry) {
 			if ( !current_user_can( 'edit_post', $entry['ID'] ) )
 				continue;