fixes an undefined index when getAccessList returns an empty array
fixes an undefined index when getAccessList returns an empty array

- [] is a valid return value that should be honored as having no access

Signed-off-by: Arthur Schiwon <9ae9918f3cbf5a90ebc25affe594cc53853aee42@arthur-schiwon.de>

nextcloud/server,nextcloud/server,nextcloud/server,nextcloud/server