[BUGFIX] Return correct available package information

The PackageManager needs to scan over all package location to be able
to decide whether a package is available or not.

Resolves: #83531
Releases: master, 8.7
Change-Id: Ib21c18a559b4c02d8efce146c8d5addf66b25f1f
Reviewed-on: https://review.typo3.org/55326


Reviewed-by: Helmut Hummel <typo3@helhum.io>
Tested-by: Helmut Hummel <typo3@helhum.io>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>