[BUGFIX] Properly display boolean values as "0" and "1" in strings

The previous implementation used two typecasts in a row: from bool
to string, and from string to bool again. This caused a boolean
false to be cast first to null and then to an empty string instead
of to "0".

Resolves: #89491
Releases: master, 9.5
Change-Id: I4003dfe1e027437fe6366d21cc05453511f85919
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62087


Tested-by: Stefan Froemken <froemken@gmail.com>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Stefan Froemken <froemken@gmail.com>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>