nsswitch wbinfo: fix uninitialised return value on error

nsswitch wbinfo: fix uninitialised return value on error

In wbinfo_lookup_sids ret was not initialised and was not set in
the error return paths. Returning an uninitialised value in the
event of an error, and in all probability something that evaluated to
true, so would not have signalled the error to the caller.

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Anoop C S <anoopcs@samba.org>