MB-10474: In case of an empty failover log

- Create a new entry in case of an empty failover log,
during warmup.

Change-Id: I42d9c5eccbb93f6679c21628228813c5e4d83fcb
Reviewed-on: http://review.couchbase.org/34702
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>