Prevent a potential OOB read in TranslateImageLine.

core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp

Index: core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp
diff --git a/core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp b/core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp
index 427abb8e37179a13f9b367540342561babadbedd..5c6a8c513f9e67f12aa89585c11f4358535622c6 100644
--- a/core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp
+++ b/core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp
@@ -27,3 +27,13 @@ TEST_F(FPDFRenderLoadImageEmbeddertest, Bug_557223) {
   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);
+}