CBD-1425:  fix same logic error in last_done_server()

Change-Id: I2b3c6a6c888b500ae3fced0328ca80b5fef4e40a
Reviewed-on: http://review.couchbase.org/41965
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>