Fix a NULL pointer crash in the CJBig2_Image copy constructor.

core/src/fxcodec/jbig2/JBig2_Image.h

 // 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
 
-#ifndef _JBIG2_IMAGE_H_
-#define _JBIG2_IMAGE_H_
+#ifndef CORE_SRC_FXCODEC_JBIG2_JBIG2_IMAGE_H_
+#define CORE_SRC_FXCODEC_JBIG2_JBIG2_IMAGE_H_
 
 #include "JBig2_Define.h"
 
 enum JBig2ComposeOp {
   JBIG2_COMPOSE_OR = 0,
   JBIG2_COMPOSE_AND = 1,
   JBIG2_COMPOSE_XOR = 2,
   JBIG2_COMPOSE_XNOR = 3,
   JBIG2_COMPOSE_REPLACE = 4
 };
 
 struct FX_RECT;
 class CJBig2_Image {
  public:
   CJBig2_Image(int32_t w, int32_t h);
 
   CJBig2_Image(int32_t w, int32_t h, int32_t stride, uint8_t* pBuf);
 
-  CJBig2_Image(CJBig2_Image& im);
+  CJBig2_Image(const CJBig2_Image& im);
 
   ~CJBig2_Image();
 
   FX_BOOL getPixel(int32_t x, int32_t y);
 
   int32_t setPixel(int32_t x, int32_t y, FX_BOOL v);
 
   void copyLine(int32_t hTo, int32_t hFrom);
 
   void fill(FX_BOOL v);
@@ skipping 36 matching lines @@
   int32_t m_nWidth;
 
   int32_t m_nHeight;
 
   int32_t m_nStride;
 
   uint8_t* m_pData;
 
   FX_BOOL m_bNeedFree;
 };
-#endif
+
+#endif  // CORE_SRC_FXCODEC_JBIG2_JBIG2_IMAGE_H_