Logout fails after enabling active_sessions

[dush]

After I've enabled active_sessions currently logged in users failed to logout with

TypeError: no implicit conversion of nil into String
  from rodauth (2.19.0) lib/rodauth/features/base.rb:649:in `digest'
  from rodauth (2.19.0) lib/rodauth/features/base.rb:649:in `compute_raw_hmac'
  from rodauth (2.19.0) lib/rodauth/features/base.rb:237:in `compute_hmac'
  from rodauth (2.19.0) lib/rodauth/features/active_sessions.rb:84:in `remove_current_session'
  from rodauth (2.19.0) lib/rodauth/features/active_sessions.rb:128:in `before_logout'
  from rodauth (2.19.0) lib/rodauth/features/logout.rb:25:in `block (4 levels) in <module:Rodauth>'

It seeems that for users logged in before enabling active_sessions session[session_id_session_key] is nil.

Note: I'm using JWT auth as it is API only Rails app.

[jeremyevans]

Thanks for the report. I agree that we should only attempt to delete if the session key is set. I'll make that change shortly.