Export 0000-00-00 00:00:00 dates as Unix time

[nestordedios]

Hi!!

When exporting content using app/nut database:export, if there are records which have automatically 0000-00-00 00:00:00 set in datecreated, datechanged or any kind of date field, the records are being exported with negative dates looking something like -0001-11-30 00:00:00.

When for instance using the Conmiex extension to migrate content from Bolt 3 to Bolt 5 at the moment of importing the record with the negative date an Exception will be thrown as the date has an incorrect value.

Maybe the incorrect exported dates could be set with the Unix time (1900-01-01 00:00:00) as the default to avoid this break everytime an export and import is made.