Multi dive edit: don't change location texts until user saves the change

If we keep updating the location text of all selected dives we can lose
the status of which dives had the same text of the original dive and which
did not (this happens if the location we are adding is identical to a
selected location but adds text to the end of it).

Now we only edit the other dives after we accepted the change.

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