Assert objnum non-zero in ReplaceIndirectObjectIfHigherGeneration()

core/fpdfapi/parser/cfdf_document.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 "core/fpdfapi/parser/cfdf_document.h"
 
 #include "core/fpdfapi/edit/cpdf_creator.h"
 #include "core/fpdfapi/parser/cpdf_dictionary.h"
@@ skipping 40 matching lines @@
 void CFDF_Document::ParseStream(IFX_SeekableReadStream* pFile, bool bOwnFile) {
   m_pFile = pFile;
   m_bOwnFile = bOwnFile;
   CPDF_SyntaxParser parser;
   parser.InitParser(m_pFile, 0);
   while (1) {
     bool bNumber;
     CFX_ByteString word = parser.GetNextWord(&bNumber);
     if (bNumber) {
       uint32_t objnum = FXSYS_atoui(word.c_str());
+      if (!objnum)
+        break;
+
       word = parser.GetNextWord(&bNumber);
       if (!bNumber)
         break;
 
       word = parser.GetNextWord(nullptr);
       if (word != "obj")
         break;
 
       CPDF_Object* pObj = parser.GetObject(this, objnum, 0, true);
       if (!pObj)
@@ skipping 23 matching lines @@
 
   buf << "%FDF-1.2\r\n";
   for (const auto& pair : *this)
     buf << pair.first << " 0 obj\r\n"
         << pair.second.get() << "\r\nendobj\r\n\r\n";
 
   buf << "trailer\r\n<</Root " << m_pRootDict->GetObjNum()
       << " 0 R>>\r\n%%EOF\r\n";
   return true;
 }