Do not do redirect handling when loggin out

Fixes #12568
Since the clearing of the execution context causes another reload. We
should not do the redirect_uri handling as this results in redirecting
back to the logout page on login.

This adds a simple middleware that will just check if the
ClearExecutionContext session variable is set. If that is the case it
will just redirect back to the login page.

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>