Planner: Change 'lasttime' only if we printed something in the plan.

This makes the 'segment' durations equal the runtime differences even when
we don't display transitions in deco.

Signed-off-by: Robert C. Helling <helling@atdotde.de>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Planner: Avoid bogus segments with 0 time

Don't show a stop if we continue at this depth.

This resolves a problem when there are more than two waypoints during deco
at the same depth. This can happen at 6m when there is a gaschange to O2
and the last stop depth is 6m (which turns the 3m stop into another 6m
stop).

Signed-off-by: Robert C. Helling <helling@atdotde.de>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>