Modified ssl_read feedback value break all the time error.

when we call this SSL_read fuction "bytes = SSL_read(ssl_socket->ssl, buf, len) ", bytes defined guint , if SSL_read fuction returns a negative number, it will be converted to a large int number, which will break all the time.

Considering the read field size of SSL，so i think change type from 'guint' to 'gint32' is enough.