[BUGFIX] Not possible to finish update wizard

When running the update wizard you are not able to finish it.
Therefore a back button is introduced when there is no
upgrade left.

Change-Id: Iaf66ced20e0dc0ec2870a559d6beee802011ae75
Resolves: #47735
Releases: 6.2
Reviewed-on: https://review.typo3.org/22679
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe