LU-6109 lfsck: check FID validity before locating object

LU-6109 lfsck: check FID validity before locating object

It is possible that the FID from iteration or linkEA is corrupted.
The LFSCK needs to check its validity before locating the object
with it to avoid falling into hung or other unexpected status.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I1df8d085bf5abf926d03882457cb8b221633d3aa
Reviewed-on: http://review.whamcloud.com/13511
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>