[BUGFIX] displayCond in flexforms broken

Fixes: #47886
Releases: 6.2, 6.1
Change-Id: I1268fce3c7e1d4c39cad029767e8503df119ea3c
Reviewed-on: https://review.typo3.org/20467
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack
Reviewed-on: https://review.typo3.org/20468