[BUGFIX] Session cookie is not recreated on login

In case login data is submitted and there is an existing cookie/session
the current session is discarded and the current cookie is unset.
Subsequently the login data is processed and login succeeds and a
new session is established, but the new cookie is not set.

Fix this be correctly remembering that we need to set a new cookie,
after we disposed the current one.

Resolves: #57751
Releases: 6.2
Change-Id: I2e4b4a381b4e557aeb95c4186c6e5365dbea442a
Reviewed-on: https://review.typo3.org/29626
Reviewed-by: Fabien Udriot
Reviewed-by: Stefan Neufeind
Reviewed-by: Robbert V
Tested-by: Robbert V
Reviewed-by: Frans Saris
Tested-by: Frans Saris
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader