Ticket #47939 - Malformed cookie for LDAP Sync makes DS crash
Bug Description: If a cookie sent from clients did not have the
expected form: server_signature#client_signature#change_info_number,
a NULL reference triggered a server crash in sync_cookie_isvalid.
Fix Description: If a cookie does not have the expected form,
sync_cookie_parse returns NULL, which prevents the NULL reference
in the server_signature and client_signature.
Reviewed by email@example.com (Thank you, Ludwig!!)
(cherry picked from commit 8f540a6cee09be13430ebe0b983d2affe2863365)