[BUGFIX] Fix the Formelement selection button on first use

Fix the Formelement selection button on first use. The variable
`propertyData` might be a string and the expression
`getCurrentlySelectedFormElement().get(propertyPath)` can return
an undefined value.
The OR operator `||` is used instead of the nullish coalescing
operator `??` on browser compatibility purpose.

Resolves: #92911
Releases: master, 10.4
Change-Id: Icd0333061edccef4ee0af00abb34dbb56306fe63
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66876


Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: waldhacker <hello@waldhacker.dev>
Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Reviewed-by: waldhacker <hello@waldhacker.dev>