LU-14474 llog: don't destroy next llog

LU-14474 llog: don't destroy next llog

do not destroy empty llog if it's referenced as
the next one in a catalog.

Lustre-change: https://review.whamcloud.com/44998
Lustre-commit: 4521f6af35d1dc20b531b87ff3633d89dbac86ec

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I78bfeb90435aaee2b8536b647aa3acec56642ea0
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/45892
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>