[TASK] Install tool: Code optimization in update wizard action

An if with only a 'throw Exception' call in it breaks code execution
and acts as a guard clause. The code below does not need to be in
an else case.

Change-Id: Ib24ed4bee06763fb46145b815a0b6f3fdf7bafa6
Resolves: #49263
Related: #49162
Releases: 6.2
Reviewed-on: https://review.typo3.org/21515
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn