LU-5398 ldlm: handle NULL lock in ldlm_handle_enqueue0()

LU-5398 ldlm: handle NULL lock in ldlm_handle_enqueue0()

In ldlm_handle_enqueue0() if ldlm_lock_create() fails then set lock to
NULL before jumping to the exit code. In the exit code test lock for
NULL rather than using IS_ERR().

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I5e2680988bd5356f2a84bd5eb9e2d40138d6d250
Reviewed-on: http://review.whamcloud.com/11197
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>