ldb-samba: ldif_read_objectSid() short-circuits without 'S'
This avoids a memcpy, and level 3 debug verbosity from
dom_sid_parse_endp().
In other places we have something like `|| in->data[1] != '-'`, but
that is not useful here -- the value is either a string SID, or a
binary SID that starts with '\1', or some awful value that we *do*
want to get messages about.
This replaces the work of ldif_comparision_objectSid_isString().
BUG: https://bugzilla.samba.org/show_bug.cgi?id=10763
Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>