JDiveLog import - add ndl=0 when on deco

This patch will add ndl='0:00 min' attribute on all the samples that
have stoptime or stopdepth set when importing from JDiveLog. This hack
ensures that dive computer's deco ceiling is shown.

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>