Minor cleanups to prevent php undefined variables warnings.

distfiles/maintform.php

@@ -11,8 +11,9 @@ include("functions.php");
 
 if (isset($_SESSION['login'])) $techid=$_SESSION['login'];
 
-$histdays=$_REQUEST['histdays'];
-$submit=$_REQUEST['submit'];
+$print=$_REQUEST['print'] ?? NULL;
+$histdays=$_REQUEST['histdays'] ?? NULL;
+$submit=$_REQUEST['submit'] ?? NULL;
 
 $logname=LOG_NAME;
 $uidtext=UID_TEXT;