Delay replot of dive so changes aren't overwritten too early

When changing tanks we triggered a replot - but that overwrote the
displayed_dive with the current_dive before the remaining data from the
displayed_dive was used to edit the current_dive.

So now we delay this until later in the function, this way copy of paste
of both tanks and weights works.

Fixes #753

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