MB-9493: Always update persistence cursor pre chk id after flush loop

Change-Id: I251ce6a56c37750c98e69a2c639349ae70460f7e
Reviewed-on: http://review.couchbase.org/30142
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>