Treat null Parent as no Parent for dictionary objects

fpdfsdk/src/fpdfppo.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
  
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "../include/fpdfppo.h"
 #include "../include/fsdk_define.h"
 
 class CPDF_PageOrganizer
@@ skipping 197 matching lines @@
         if(!pParent || pParent->GetType() != PDFOBJ_DICTIONARY) return NULL;
         
         CPDF_Dictionary* pp = (CPDF_Dictionary*)pParent;
         
         if(pDict->KeyExist((const char*)nSrctag))       
                 return pDict->GetElement((const char*)nSrctag);
         while (pp)
         {
                 if(pp->KeyExist((const char*)nSrctag))  
                         return pp->GetElement((const char*)nSrctag);
-                else if(pp->KeyExist("Parent"))
+                else if (pp->KeyExist("Parent"))
+                {
                         pp = (CPDF_Dictionary*)pp->GetElement("Parent")->GetDirect();
+                        if (pp->GetType() == PDFOBJ_NULL) break;
+                }
                 else break;
         }
         
         return NULL;
 }
 
 FX_BOOL CPDF_PageOrganizer::UpdateReference(CPDF_Object *pObj, CPDF_Document *pDoc, 
                                                                                  CFX_MapPtrToPtr* pMapPtrToPtr)
 {
         switch (pObj->GetType())
@@ skipping 222 matching lines @@
         if(!pSrcDict)
                 return FALSE;
         CPDF_Document* pDstDoc = (CPDF_Document*)dest_doc;
         CPDF_Dictionary* pDstDict = pDstDoc->GetRoot();
         if(!pDstDict)
                 return FALSE;
         pDstDict->SetAt(FX_BSTRC("ViewerPreferences"), pSrcDict->Clone(TRUE));
         return TRUE;
 }