LU-5865 lfsck: avoid NULL pointer

NOT pass "NULL" as the parameter of @lmv for lfsck_record_lmv(),
then the subsequent handling inside lfsck_record_lmv() needs NOT
to worry about the case of "lmv == NULL".

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I5f308818edd5ded2c4ccc7d59fb0908791b8aae3
Reviewed-on: http://review.whamcloud.com/12597
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>