Fix for the "Missing date in title" errors of the korina harvester

The "Missing date in title" error in the korina harvester occured due to two entries in the news section which don't even have titles. As such entries shouldn't be listed in umwelt.info to begin with (title should always be present), the new version now checks if the datum exists. If not, no data set will be written and a simple warning instead of an error will be displayed.