Fix typo that broke gas reporting in dive list

The brainless idiot who implemented commit c539c8f86192 ("Remove the .used
member of the cylinder structure") clearly worked on the basis of "it
compiles, it must be perfect".

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Planner: don't redo the plan after partial edits of GFlow/high

In most cases this wouldn't really matter, but when planning very deep or
very long dive with corresponding very long deco times, calculating the
deco takes long enough to make this notable.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>