xfs_quota: print quota id number if the name can't be found

xfs_quota: print quota id number if the name can't be found

When use GETNEXTQUOTA ioctl to report project quota, it always
report an unexpected quota:

  (null) 0 0 0 00 [--------]

The ID 0 store the default quota, even if no one set default quota,
it still have quota accounting, but not enforced. So GETNEXTQUOTA
can find and report this undefined quota.

From this problem, I thought if others' quota name miss, (null) will
be printed too. e.g.

  # xfs_quota -xc "limit -u bsoft=300m bhard=400m test" $mnt
  # xfs_quota -xc "report -u" $mnt
  User ID          Used       Soft       Hard    Warn/Grace
  ---------- --------------------------------------------------
  root                0          0          0     00 [--------]
  test                0     307200     409600     00 [--------]
  # userdel -r test
  # xfs_quota -xc "report -u" $mnt
  User ID          Used       Soft       Hard    Warn/Grace
  ---------- --------------------------------------------------
  root                0          0          0     00 [--------]
  (null)              0     307200     409600     00 [--------]

So this problem same with above id 0's problem. To deal with this,
this patch will print id number if the name can't be found.

However, if we use the old GETQUOTA ioctl, it won't print project id
0 quota information if it's not defined. That's different with
GETNEXTQUOTA. For keep consistent, this patch also print project id
0 when use old GETQUOTA.

Signed-off-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>