Fix encrypt_cookie and sign_cookie when controller is nil

[peterzhu2118]

If you enable eager loading or try to use the UserSession model before the first request, Authlogic::Session::Base.controller is not initialized so if you set sign_cookie or encrypt_cookie, it will crash.

[tiegz]

Makes sense to me, how about you @jaredbeck ?

[jaredbeck]

It seems fine to merge as is, but (bikeshedding) I think the error message could be better. I think the current message will be "Signed cookies not supported with NilClass". A better message would be "Authlogic has not been activated yet, so the sign_cookie option cannot be set", or something like that.

Edit: On second thought, my suggestion re: error message doesn't make sense, and I've merged this as is.