sip_www_authenticate is NULL during auth challenge

[fredldotme]

The Ubuntu archive hosts Telepathy-Rakia & the unmaintained sofia-sip right now.

When Telepathy-Rakia is used together with this maintained branch of sofia-sip, it returns a priv_handle_auth: no realm presented for authentication error during authentication attempts.

https://github.com/TelepathyIM/telepathy-rakia/blob/master/src/sip-connection.c#L690

As it seems the sip_www_authenticate member is NULL even though the recvmsg() has gotten WWW-Authenticate: Digest realm=\"the.sip.host\" as per strace, indicating that something is swallowing or not setting the appropriate data from the header.