[CLEANUP] FAL code

* Remove absolute namespaces where not necessary
* Define undefined class members and variables
* Add type checks before calling methods

Resolves: #72578
Releases: master
Change-Id: Ie0295be3693885b4ed2386877790d205291a1085
Reviewed-on: https://review.typo3.org/45628


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>