[BUGFIX] StandaloneView must not require ucfirst file names

Regression to #61361.
There's no reason to require ucfirst file names for Layouts and Partials.

Resolves: #63367
Releases: 6.2
Change-Id: I3b931a0ef129c88388d427685af47ebb3e4a355f
Reviewed-on: http://review.typo3.org/34705
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Stefan Froemken <froemken@gmail.com>
Tested-by: Stefan Froemken <froemken@gmail.com>
Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>