[BUGFIX] Only scan package base paths if subdirectories exist

Include possible package base paths only if subdirectories are available.
Otherwise no extension can be found in the base path anyway.

Resolves: #83070
Releases: master, 8.7, 7.6
Change-Id: I503623c607554a60bd144c83e3f69e78fe5a7ea0
Reviewed-on: https://review.typo3.org/55018


Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>