[BUGFIX] Make loading of depth in workspace module work for 0

The implementation of storing the depth selection in the
workspace module did not account for the "This site"
option and the according value "0".

With this patch now all options of the depth selector can
be stored and loaded from UC.

Resolves: #88168
Releases: master, 9.5
Change-Id: I21ea3a4e300dbb71516679ea9f5ac901364b0c4c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60508


Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Achim Fritz <af@achimfritz.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Achim Fritz <af@achimfritz.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>