Fix Jbig2 document context creation by checking proper pointer

pdfium.gyp

 # Copyright 2015 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.
 
 {
   'variables': {
     'chromium_code': 1,
     'pdf_use_skia%': 0,
     'pdf_enable_v8%': 1,
     'pdf_enable_xfa%': 0, # Set to 1 by standalone.gypi in a standalone build.
@@ skipping 953 matching lines @@
         'pdfium',
         'test_support',
       ],
       'sources': [
         'core/fpdfapi/fpdf_page/fpdf_page_func_embeddertest.cpp',
         'core/fpdfapi/fpdf_parser/cpdf_parser_embeddertest.cpp',
         'core/fpdfapi/fpdf_parser/cpdf_security_handler_embeddertest.cpp',
         'core/fpdfapi/fpdf_parser/fpdf_parser_decode_embeddertest.cpp',
         'core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp',
         'core/fpdfapi/fpdf_render/fpdf_render_pattern_embeddertest.cpp',
+        'core/fxcodec/codec/fx_codec_embeddertest.cpp',
         'core/fxge/ge/fx_ge_text_embeddertest.cpp',
         'fpdfsdk/fpdf_dataavail_embeddertest.cpp',
         'fpdfsdk/fpdfdoc_embeddertest.cpp',
         'fpdfsdk/fpdfedit_embeddertest.cpp',
         'fpdfsdk/fpdfext_embeddertest.cpp',
         'fpdfsdk/fpdfformfill_embeddertest.cpp',
         'fpdfsdk/fpdfsave_embeddertest.cpp',
         'fpdfsdk/fpdftext_embeddertest.cpp',
         'fpdfsdk/fpdfview_c_api_test.c',
         'fpdfsdk/fpdfview_c_api_test.h',
@@ skipping 119 matching lines @@
             'fpdfsdk/fpdfxfa/include/fpdfxfa_app.h',
             'fpdfsdk/fpdfxfa/include/fpdfxfa_doc.h',
             'fpdfsdk/fpdfxfa/include/fpdfxfa_page.h',
             'fpdfsdk/fpdfxfa/include/fpdfxfa_util.h',
           ],
         },
       ]
     }],
   ]
 }