[BUGFIX] Fix insufficient constraint

Fix insufficient constraint while lookup user for login after create.
Resolves: #63035
Releases: master,6.2

Change-Id: I16978cb2ec88f01321337ef8a1e2b74d2471a895
Reviewed-on: http://review.typo3.org/34370
Reviewed-by: Alex Kellner <alexander.kellner@einpraegsam.net>
Tested-by: Alex Kellner <alexander.kellner@einpraegsam.net>