Fix Jbig2 document context creation by checking proper pointer

core/fxcodec/codec/fx_codec_embeddertest.cpp

 // Copyright 2016 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.
 
 #include "testing/embedder_test.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-class FXGETextEmbedderTest : public EmbedderTest {};
+class FXCodecEmbeddertest : public EmbedderTest {};
 
-TEST_F(FXGETextEmbedderTest, BadItalic) {
-  // Shouldn't crash.
-  EXPECT_TRUE(OpenDocument("bug_601362.pdf"));
+TEST_F(FXCodecEmbeddertest, Bug_631912) {
+  // Test jbig2 image in PDF file can be loaded successfully.
+  // Should not crash.
+  EXPECT_TRUE(OpenDocument("bug_631912.pdf"));
   FPDF_PAGE page = LoadPage(0);
   EXPECT_NE(nullptr, page);
   FPDF_BITMAP bitmap = RenderPage(page);
   FPDFBitmap_Destroy(bitmap);
   UnloadPage(page);
 }