AC-2892: fix return types in Zend_Pdf

- Rollback argument value update

Author: xmav

library/Zend/Pdf/Element/Reference.php

@@ -94,11 +94,6 @@ public function __construct(
         Zend_Pdf_Element_Reference_Context $context,
         Zend_Pdf_ElementFactory $factory
     ){
-        // This was changed as PHP8 errors out if there's an optional parameter before a required param
-        if (empty($genNum)) {
-            $genNum = 0;
-        }
-
         if ( !(is_integer($objNum) && $objNum > 0) ) {
             #require_once 'Zend/Pdf/Exception.php';
             throw new Zend_Pdf_Exception('Object number must be positive integer');