Bug 33815: Do not explode if logged in user modify their own userid

Bug 33815: Do not explode if logged in user modify their own userid

If the logged in librarian modifies their own userid they will get the
following error when submitting the form:
Can't call method "password_expired" on an undefined value at /kohadevbox/koha/C4/Auth.pm line 1780

We could handle this situation and flag the session as expired. Better
would be to deal with this specific user case and update the cookie (?)

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: David Cook <dcook@prosentient.com.au>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>