[BUGFIX] Allow record insert on rootlevel

The DataHandler function checkRecordInsertAccess() does
now check the configuration for the root level.

Resolves: #52386
Releases: 6.2, 6.1, 6.0
Change-Id: I1810ea847e631ea6b242346a0271f491fd60fdf9
Reviewed-on: https://review.typo3.org/24166
Reviewed-by: Leon de Rijke
Tested-by: Leon de Rijke
Reviewed-by: Markus Klein
Tested-by: Markus Klein