Make _libssh2_sftp_read() fully non-blocking safe.  This makes libssh2_sftp_readnb() non-blocking safe and libssh2_sftp_read() blocking safe
Make _libssh2_sftp_read() fully non-blocking safe.  This makes
libssh2_sftp_readnb() non-blocking safe and libssh2_sftp_read() blocking
safe

libssh2/libssh2,libssh2/libssh2,libssh2/libssh2,libssh2/libssh2