[BUGFIX] Fix error where tsconf_alphaSort is undefined

When a user opens Info -> Page TSconfig it will throw
an error "Undefined array key tsconf_alphaSort".

Fixed by adding 0 as fallback to the array access.
Another test was added which checks if modules in the
toolbar dropdown are callable.

Resolves: #94392
Releases: master
Change-Id: I2e1f2e4b687155fa1d1c13791f46f10915c834f9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/69536


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>