in the attempt to fix 627393, changed IFX_FileRead's readBlock to return the length it reads

core/fxcodec/codec/fx_codec_tiff.cpp

 // 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
 
 #include <limits>
 
 #include "core/fxcodec/codec/codec_int.h"
 #include "core/fxcodec/fx_codec.h"
@@ skipping 80 matching lines @@
 namespace {
 
 tsize_t tiff_read(thandle_t context, tdata_t buf, tsize_t length) {
   CCodec_TiffContext* pTiffContext =
       reinterpret_cast<CCodec_TiffContext*>(context);
   FX_SAFE_UINT32 increment = pTiffContext->offset();
   increment += length;
   if (!increment.IsValid())
     return 0;
 
-  if (!pTiffContext->io_in()->ReadBlock(buf, pTiffContext->offset(), length))
+  size_t readSize =
+      pTiffContext->io_in()->ReadBlock(buf, pTiffContext->offset(), length);
+  if (readSize != static_cast<size_t>(length) &&
+      !pTiffContext->io_in()->IsEOF())
     return 0;
 
-  pTiffContext->set_offset(increment.ValueOrDie());
-  return length;
+  pTiffContext->set_offset(increment.ValueOrDie() - length + readSize);
+  return readSize;
 }
 
 tsize_t tiff_write(thandle_t context, tdata_t buf, tsize_t length) {
   ASSERT(false);
   return 0;
 }
 
 toff_t tiff_seek(thandle_t context, toff_t offset, int whence) {
   CCodec_TiffContext* pTiffContext =
       reinterpret_cast<CCodec_TiffContext*>(context);
@@ skipping 362 matching lines @@
 }
 
 bool CCodec_TiffModule::Decode(CCodec_TiffContext* ctx,
                                class CFX_DIBitmap* pDIBitmap) {
   return ctx->Decode(pDIBitmap);
 }
 
 void CCodec_TiffModule::DestroyDecoder(CCodec_TiffContext* ctx) {
   delete ctx;
 }