LU-10504 flr: check layout pointer before using it

LU-10504 flr: check layout pointer before using it

This patch fixes mirror_create() to check layout pointer
before using it.

Change-Id: Ia1454b5c7fcfcee227d0b954a477cefe5d7bb5f7
Test-Parameters: trivial testlist=sanity-flr
Signed-off-by: Jian Yu <jian.yu@intel.com>
Reviewed-on: https://review.whamcloud.com/30915
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>