[BUGFIX] Prevent TypeError in FileSearchDemand

Since `QueryHelper::parseOrderBy()` might return
NULL as value for fieldname and direction, we
now check those values properly to prevent any
TypeErrors using the type-hinted `addOrdering()`
method.

Resolves: #102649
Releases: main, 12.4
Change-Id: Ie117e7fd0593392e843aaca5c1e9c254c4de42d1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82129


Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>