Fix Jbig2 document context creation by checking proper pointer

core/fxcodec/codec/fx_codec_jbig.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/fxcodec/codec/ccodec_jbig2module.h"
 
 #include <list>
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_stream_acc.h"
 #include "core/fxcodec/include/JBig2_DocumentContext.h"
 #include "core/fxcodec/jbig2/JBig2_Context.h"
 #include "core/fxcodec/jbig2/JBig2_Image.h"
 #include "core/fxcrt/include/fx_memory.h"
 
 JBig2_DocumentContext::JBig2_DocumentContext() {}
 
 JBig2_DocumentContext::~JBig2_DocumentContext() {}
 
 JBig2_DocumentContext* GetJBig2DocumentContext(
     std::unique_ptr<JBig2_DocumentContext>* pContextHolder) {
-  if (!pContextHolder)
+  if (!pContextHolder->get())
     pContextHolder->reset(new JBig2_DocumentContext());
   return pContextHolder->get();
 }
 
 CCodec_Jbig2Context::CCodec_Jbig2Context()
     : m_width(0),
       m_height(0),
       m_pGlobalStream(nullptr),
       m_pSrcStream(nullptr),
       m_dest_buf(0),
@@ skipping 61 matching lines @@
   pJbig2Context->m_pContext.reset();
   if (ret != JBIG2_SUCCESS)
     return FXCODEC_STATUS_ERROR;
 
   int dword_size = pJbig2Context->m_height * pJbig2Context->m_dest_pitch / 4;
   uint32_t* dword_buf = (uint32_t*)pJbig2Context->m_dest_buf;
   for (int i = 0; i < dword_size; i++)
     dword_buf[i] = ~dword_buf[i];
   return FXCODEC_STATUS_DECODE_FINISH;
 }