Set REQUEST variables to default to NULL if not passed to avoid php warnings

distfiles/parts.php

@@ -15,10 +15,10 @@ if (isset($_SESSION['login'])) {
     unset($loggedin);
 }
 
-$print=$_REQUEST['print'];
-$add=$_REQUEST['add'];
-$sort=$_REQUEST['sort'];
-$order=$_REQUEST['order'];
+$print=$_REQUEST['print'] ?? NULL;
+$add=$_REQUEST['add'] ?? NULL;
+$sort=$_REQUEST['sort'] ?? NULL;
+$order=$_REQUEST['order'] ?? NULL;
 
 $logname=LOG_NAME;
 $uidtext=UID_TEXT;