When copying dives, make copies of samples/events in first DC

We carefully copied the dive computers and their samples and events, but
only for the second and later DCs. For the first DC we simply copied the
pointers but not what they were pointing at. So when the copied dive was
freed, those pointers in the original went to freed memory.

Not good.

Fixes #599

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