[FOLLOWUP] Class loader handles invalid classes

The check if we have class information
can be simplified to !empty()

Resolves: #57117
Related: #56933
Releases: 6.2
Change-Id: I8532b26142cc39da2b9bcca9880df715da57d59e
Reviewed-on: https://review.typo3.org/28596
Reviewed-by: Frans Saris
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Stefan Neufeind
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel