LU-13992 llite: ASSERTION( last_oap_count > 0 ) failed

LU-13992 llite: ASSERTION( last_oap_count > 0 ) failed

Punch uses o_blocks to send end of a region. So it
can be mixed with real blocks count on error.

Update blocks count only on success.

Change-Id: I86241c4e5723079b20401805b853d356130f58d9
HPE-bug-id: LUS-7407
Test-Parameters: fstype=zfs
Signed-off-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Andrew Perepechko <c17827@cray.com>
Reviewed-by: Alexander Boyko <c17825@cray.com>
Tested-by: Elena Gryaznova <c17455@cray.com>
Reviewed-on: https://review.whamcloud.com/40050
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.super@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>