[BUGFIX] Default value for native datetime fields must not be 0

The default database value for native fields of type datetime
must not be 0 but NULL.

Resolves: #79304
Releases: master, 8.7
Change-Id: I823a85be2a01ccd8df4997ab2969b2c95ed78cd1
Reviewed-on: https://review.typo3.org/51296


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>