Prevent a potential OOB read in TranslateImageLine.

core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp

 // 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.
 
 #include "testing/embedder_test.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 class FPDFRenderLoadImageEmbeddertest : public EmbedderTest {};
 
 TEST_F(FPDFRenderLoadImageEmbeddertest, Bug_554151) {
   // Test scanline downsampling with a BitsPerComponent of 4.
   // Should not crash.
   EXPECT_TRUE(OpenDocument("bug_554151.pdf"));
   FPDF_PAGE page = LoadPage(0);
   EXPECT_NE(nullptr, page);
   FPDF_BITMAP bitmap = RenderPage(page);
   FPDFBitmap_Destroy(bitmap);
   UnloadPage(page);
 }
 
 TEST_F(FPDFRenderLoadImageEmbeddertest, Bug_557223) {
   // Should not crash
   EXPECT_TRUE(OpenDocument("bug_557223.pdf"));
   FPDF_PAGE page = LoadPage(0);
   EXPECT_NE(nullptr, page);
   FPDF_BITMAP bitmap = RenderPage(page);
   FPDFBitmap_Destroy(bitmap);
   UnloadPage(page);
 }
+
+TEST_F(FPDFRenderLoadImageEmbeddertest, Bug_603518) {
+  // Should not crash
+  EXPECT_TRUE(OpenDocument("bug_603518.pdf"));
+  FPDF_PAGE page = LoadPage(0);
+  EXPECT_NE(nullptr, page);
+  FPDF_BITMAP bitmap = RenderPage(page);
+  FPDFBitmap_Destroy(bitmap);
+  UnloadPage(page);
+}