If you switch the user although you are in the su mode,
and you switch back you are the user from the su mode.

Resolves: #73797
Releases: master, 7.6
Change-Id: Idc10d6afbead80f79f4b51f49a4c52eab7c23456
Reviewed-on: https://review.typo3.org/46981


Reviewed-by: Matthias Vogel <typo3@kanti.de>
Tested-by: Matthias Vogel <typo3@kanti.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>