Prevent notice script_name not defined

> ( ! )</span> Notice: Undefined index: SCRIPT_NAME in endor/piwik/piwik-php-tracker/PiwikTracker.php on line <i>1815</i>

PiwikTracker.php

@@ -1811,7 +1811,7 @@ class PiwikTracker
                 }
             }
         }
-        if (empty($url)) {
+        if (empty($url) && isset($_SERVER['SCRIPT_NAME'])) {
             $url = $_SERVER['SCRIPT_NAME'];
         }