[BUGFIX] Make EXT:filemetadata work with MySQL strict mode

EXT:filemetadata delivers a lot of sys_file_metadata fields
with NOT NULL in it, which does not make sense.

MySQL strict mode does not work with this SQL definition.

Resolves: #77418
Releases: master, 7.6
Change-Id: Ia93c3fd88066ba148b26eb8044fa297d8572c86f
Reviewed-on: https://review.typo3.org/49389


Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Thomas Schlumberger <thomas@b13.de>
Tested-by: Thomas Schlumberger <thomas@b13.de>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>