http async client example doesn't close on error correctly

[Frank <fhriley@…>]

In handle_connect, the final else block needs a "socket_.close();"

[chris_kohlhoff]

Actually it is not required since no further asynchronous operations are started. The socket will then be closed automatically when the class's destructor runs. In any case, the example has since been converted to use the asio::async_connect() function, which has simplified the example logic somewhat.