crash on divelogs.de export

[Miika Turkia]

Hello,

Subsurface crashes under certain circumstances when exporting to
divelogs.de. So far I haven't been able to figure out what is going
wrong so here are the steps to reproduce with beta 1:
- start subsurface: subsurface dives/test21.xml dives/test22.xml
- hit OK for the nagging dialog about old log version
- select all: ctrl-a (or any other method)
- go to export: ctrl-e
- select divelogs.de (alt-v)
- OK
=> crash

miika