added an exception after redirection

Throwing an exception here because javascript continues to execute after
the redirect until the new page actually loads. The exception halts
promise resolution which fixes type errors on inital unauthed page load.

joe/topic/JI-486-auth-redirect-race-condition
Merge pull request #1 from janrain/joe/topic/JI-486-auth-redirect-race-condition

added an exception after redirection