message: build: eliminate Win32 warnings
diff: @@ -160,7 +160,7 @@ public:
  break;
  }
  new_pos = std::min(new_pos, size);
  - decoder->m_buf_pos = new_pos;
  + decoder->m_buf_pos = (size_t)new_pos;
  return new_pos;
  }
  @@ -613,7 +613,7 @@ public:
  static tmsize_t write( thandle_t handle, void* buffer, tmsize_t n )
  {
  TiffEncoderBufHelper *helper = reinterpret_cast<TiffEncoderBufHelper*>(handle);
  - size_t begin = helper->m_buf_pos;
  + size_t begin = (size_t)helper->m_buf_pos;
  size_t end = begin + n;
  if ( helper->m_buf->size() < end )
  {
  