Fix too strict check on validity of template name

 - use preg_match instead of ctype_alnum, because _ is allowed as well

website_code/php/templates/duplicate_template.php

@@ -64,7 +64,7 @@
 $folder_id = x_clean_input($_POST['folder_id']);
 $template_name = x_clean_input($_POST['template_name']);
 
-if (!ctype_alnum($template_name))
+if (!preg_match('/^[a-zA-Z0-9_]+$/',$template_name))
 {
     die("Invalid template name");
 }