idmap_autorid: fix traversal of ranges to correctly exclude mapping records.

idmap_autorid: fix traversal of ranges to correctly exclude mapping records.

When listing all ranges with "net idmap get ranges", the database records
of the form "S-1-5-10" --> "GID 100016" were treated here as rangee mapings,
resulting in an faulty printout like this: "RANGE 541346119: S-1-5-10".

This patch fixes this by adding a filter that checks the size of the
value datablob.

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Mon Oct 21 19:48:40 CEST 2013 on sn-devel-104