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

fpdfsdk/include/fsdk_define.h

Index: fpdfsdk/include/fsdk_define.h
diff --git a/fpdfsdk/include/fsdk_define.h b/fpdfsdk/include/fsdk_define.h
index cb4e5c34a6b05cedb53a115ae00fe3c970742765..b665b42465820b2fb5d81981acdf9631678775ff 100644
--- a/fpdfsdk/include/fsdk_define.h
+++ b/fpdfsdk/include/fsdk_define.h
@@ -33,7 +33,8 @@ class CPDF_CustomAccess final : public IFX_FileRead {
   // IFX_FileRead
   FX_FILESIZE GetSize() override;
   void Release() override;
-  FX_BOOL ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override;
+  FX_BOOL IsEOF() override;
+  size_t ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override;
 
 #ifdef PDF_ENABLE_XFA
   virtual CFX_ByteString GetFullPath();
@@ -43,6 +44,7 @@ class CPDF_CustomAccess final : public IFX_FileRead {
 
  private:
   FPDF_FILEACCESS m_FileAccess;
+  FX_FILESIZE m_nCurPos;
 #ifdef PDF_ENABLE_XFA
   uint8_t m_Buffer[512];
   uint32_t m_BufferOffset;
@@ -61,7 +63,7 @@ class CFPDF_FileStream : public IFX_FileStream {
   FX_FILESIZE GetSize() override;
   FX_BOOL IsEOF() override;
   FX_FILESIZE GetPosition() override;
-  FX_BOOL ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override;
+  size_t ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override;
   size_t ReadBlock(void* buffer, size_t size) override;
   FX_BOOL WriteBlock(const void* buffer,
                      FX_FILESIZE offset,