Fixes #1751: Check for defined constant before use - php8.x

vtlib/Vtiger/Utils.php

@@ -303,7 +303,7 @@ class Vtiger_Utils {
      * @param <boolean> $request flag to enable or disable request in log
      */
     static function ModuleLog($module, $mixed, $extra = array()) {
-        if (ALLOW_MODULE_LOGGING) { 
+        if (defined('ALLOW_MODULE_LOGGING')) { 
             global $site_URL;
             $date = date('Y-m-d H:i:s');
             $log = array($site_URL,$module, $date);