Fix crash bug when saving credentials with no Kerberos auth data.

Fix crash bug when saving credentials with no Kerberos auth data.

scheduler/client.c:
    - cupsdReadClient(): Reset gss_have_creds to 0.

scheduler/client.h:
    - Add gss_have_creds to cupsd_client_s.

scheduler/ipp.c:
    - save_auth_info(): Only call save_krb5_creds() if we have credential
      info, and clear previous info if it is available for that job.

scheduler/auth.c:
    - cupsdAuthorize(): Set gss_have_creds to 1 on a successful GSS
      negotiation.

git-svn-id: svn+ssh://src.apple.com/svn/cups/cups.org/trunk@6570 7a7537e8-13f0-0310-91df-b6672ffda945