cliopts: don't assign progname if NULL

Logic should be inverted

Change-Id: Iec46673a75801adff5a565dd361255611f427e3a
Reviewed-on: http://review.couchbase.org/39094
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>