Assert objnum non-zero in ReplaceIndirectObjectIfHigherGeneration()

core/fpdfapi/parser/cpdf_parser.cpp

 // Copyright 2016 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 "core/fpdfapi/parser/cpdf_parser.h"
 
 #include <vector>
 
@@ skipping 942 matching lines @@
   m_SortedOffset.insert(last_trailer - m_pSyntax->m_HeaderOffset);
   return m_pTrailer && !m_ObjectInfo.empty();
 }
 
 bool CPDF_Parser::LoadCrossRefV5(FX_FILESIZE* pos, bool bMainXRef) {
   std::unique_ptr<CPDF_Object> pObject(
       ParseIndirectObjectAt(m_pDocument, *pos, 0));
   if (!pObject)
     return false;
 
+  uint32_t objnum = pObject->m_ObjNum;
+  if (!objnum)
+    return false;
+
   CPDF_Object* pUnownedObject = pObject.get();
-
   if (m_pDocument) {
     CPDF_Dictionary* pRootDict = m_pDocument->GetRoot();
-    if (pRootDict && pRootDict->GetObjNum() == pObject->m_ObjNum)
+    if (pRootDict && pRootDict->GetObjNum() == objnum)
       return false;
     // Takes ownership of object (std::move someday).
-    uint32_t objnum = pObject->m_ObjNum;
     if (!m_pDocument->ReplaceIndirectObjectIfHigherGeneration(
             objnum, pObject.release())) {
       return false;
     }
   }
 
   CPDF_Stream* pStream = pUnownedObject->AsStream();
   if (!pStream)
     return false;
 
@@ skipping 638 matching lines @@
   if (!LoadLinearizedAllCrossRefV4(m_LastXRefOffset, m_dwXrefStartObjNum) &&
       !LoadLinearizedAllCrossRefV5(m_LastXRefOffset)) {
     m_LastXRefOffset = 0;
     m_pSyntax->m_MetadataObjnum = dwSaveMetadataObjnum;
     return FORMAT_ERROR;
   }
 
   m_pSyntax->m_MetadataObjnum = dwSaveMetadataObjnum;
   return SUCCESS;
 }