LU-2868 lfsck: finish otable iteration if no more objects

LU-2868 lfsck: finish otable iteration if no more objects

If there are no objects to be scanned just at the LFSCK beginning,
then the LFSCK should mark the otable-based iteration as finished
to avoid to access non-initialized data via dt_it_ops::rec().

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I67e880ccfa13e867c4ca7f1858d67909ba0415b3
Reviewed-on: http://review.whamcloud.com/5622
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>