Fix null crash in CheckTrailer.

core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.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/fpdfapi/fpdf_parser.h"
 #include "../../../include/fpdfapi/fpdf_module.h"
 #include "../../../include/fpdfapi/fpdf_page.h"
 #include "../../../../third_party/numerics/safe_math.h"
@@ skipping 3810 matching lines @@
         if (!pBuf) {
             m_docStatus = PDF_DATAAVAIL_ERROR;
             return FALSE;
         }
         if (!m_pFileRead->ReadBlock(pBuf, m_dwTrailerOffset, iSize)) {
             return FALSE;
         }
         CFX_SmartPointer<IFX_FileStream> file(FX_CreateMemoryStream(pBuf, (size_t)iSize, FALSE));
         m_syntaxParser.InitParser((IFX_FileStream*)file, 0);
         CPDF_Object *pTrailer = m_syntaxParser.GetObject(NULL, 0, 0, 0);
-        if (pTrailer->GetType() != PDFOBJ_DICTIONARY) {
-            return FALSE;
-        }
         if (!pTrailer) {
             m_Pos += m_syntaxParser.SavePos();
             pHints->AddSegment(m_Pos, iTrailerSize);
             return FALSE;
         }
+        if (pTrailer->GetType() != PDFOBJ_DICTIONARY) {
+            return FALSE;
+        }
         CPDF_Dictionary *pTrailerDict = pTrailer->GetDict();
         if (pTrailerDict) {
             CPDF_Object *pEncrypt = pTrailerDict->GetElement("Encrypt");
             if (pEncrypt && pEncrypt->GetType() == PDFOBJ_REFERENCE) {
                 m_docStatus = PDF_DATAAVAIL_LOADALLFILE;
                 pTrailer->Release();
                 return TRUE;
             }
         }
         FX_DWORD xrefpos = GetDirectInteger(pTrailer->GetDict(), FX_BSTRC("Prev"));
@@ skipping 577 matching lines @@
 {
     FX_INT32 iSize = m_childNode.GetSize();
     for (FX_INT32 i = 0; i < iSize; ++i) {
         CPDF_PageNode *pNode = (CPDF_PageNode*)m_childNode[i];
         if (pNode) {
             delete pNode;
         }
     }
     m_childNode.RemoveAll();
 }