When editing a dive, a DiveObjectHelper of the unmodified dive
was created to compare the edited with the old values. Since
the DiveObjectHelper is used here only as a pointless wrapper
around the formatting functions, call these functions directly.
However, note that the code is in principle wrong since the
change to the mobile-models, which do not use the DiveObjectHelper.
The real fix would be to reload the data from the model to prevent
going out-of-sync with respect to the formatting routines!
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>