For already registered users, plan is triggered again

[ptruessel]

If I already have an account (whether paid or free), I should not be able to make any further bookings via plans. Visiting the plan page triggers a session, which is then assigned to the user. The user then logs in and is redirected to the payment page or the default plan is activated.

If a user already has a plan activated and logs in with a redirect session, they must be redirected to the plans without activating anything.