Simplify krb5_cccol_have_content()

Simplify krb5_cccol_have_content()

For the purposes of determining whether Kerberos credentials are
present, just check for an initialized ccache (as detected by
krb5_cc_get_principal()), not one with credentials in it.  For KCM and
KEYRING caches, this changes avoids the O(n) expense of starting an
iteration.

Also fix a potential memory leak if a cache is found after an error is
saved.

ticket: 8998 (new)