LU-7061 osd-ldiskfs: NULL pointer dereference in osd_scrub_refresh_mapping

LU-7061 osd-ldiskfs: NULL pointer dereference in osd_scrub_refresh_mapping

id can be NULL for DTO_INDEX_DELETE operation.

Change-Id: I0ead24b8d9112d65b48b8d96d93181fa17d04c49
Xyratex-bug-id: MRP-2431
Signed-off-by: Andriy Skulysh <andriy.skulysh@seagate.com>
Reviewed-on: http://review.whamcloud.com/16138
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>