CVE-2019-14861: s4-rpc/dnsserver: Avoid crash in ldb_qsort() via dcesrv_DnssrvEnumRec...

CVE-2019-14861: s4-rpc/dnsserver: Avoid crash in ldb_qsort() via dcesrv_DnssrvEnumRecords)

dns_name_compare() had logic to put @ and the top record in the tree being
enumerated first, but if a domain had both then this would break the
older qsort() implementation in ldb_qsort() and cause a read of memory
before the base pointer.

By removing this special case (not required as the base pointer
is already seperatly located, no matter were it is in the
returned records) the crash is avoided.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14138

Signed-off-by: Andrew Bartlett <abartlet@samba.org>