[BUGFIX] Initialize uploadfolder key for TCA group file_reference

The array key 'uploadfolder' is initialized on a non existing array.
It must be initialized on the processed tca array

Resolves: #81681
Releases: master, 8.7
Change-Id: Ied776e4b0d0d4c33cf0894a2c4c95ceb6c03bb18
Reviewed-on: https://review.typo3.org/53341


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>