Bug 34513: Set auth state correctly when changing auth sessions

Bug 34513: Set auth state correctly when changing auth sessions

This patch sets the $auth_state to failed when changing auth sessions,
so that the new login attempt gets processed correctly (instead
of skipping the authorization step).

Test plan:
0. Apply the patch
1. koha-plack --reload kohadev
2. Go to
http://localhost:8081/cgi-bin/koha/admin/preferences.pl?tab=&op=search&searchfield=baseurl
3. Log in as an OPAC user with 0 permissions
4. Note the auth screen "Error: You do not have permission to access this page"
5. Click "Log in"
6. Note that you're still shown a login screen (and that you've been logged out of
your previous authenticated session)

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>