boost::asio::async_read_at not returning boost::asio::error::eof

[Lloyd]

in the boost::asio::async_read_at handler it is not returning boost::asio::error::eof as "error" (when reaches the end of file) instead we had to check error against "error==boost::system::windows_error::handle_eof"

[chris_kohlhoff]

This was already fixed for boost 1.42.