[BUGFIX] getFolderStatus ajax also being called in Step Installer

Resolves: #57262
Releases: 6.2
Change-Id: I190420ef696de819ebf3f06033ba7e97c639a92c
Reviewed-on: https://review.typo3.org/28739
Reviewed-by: Alexander Opitz
Tested-by: Alexander Opitz
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn