staging/lustre/lov: don't crash accessing LOV object with FID{0, 0}

Some object maybe has a corrupted LOV EA or a hole in
LOV EA. We should not crash client in such case.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-on: http://review.whamcloud.com/12740
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4958
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>