spoolss: clear JobInfo on GetJob error

spoolss: clear JobInfo on GetJob error

In handling a spoolss GetJob request, the _spoolss_GetJob() handler may
return an immediate error if one of the input parameters is invalid. If
this is done without zeroing the pre-allocated @info pointer, then
api_spoolss_GetJob() will attempt to marshall @info, which in the case
of an @offered value of zero results in a marshalling error:

ndr_push_error(7): Bad subcontext (PUSH) content_size 64 is larger
than size_is(0)

Bug: https://bugzilla.samba.org/show_bug.cgi?id=10984

Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>