You cannot quit if a session expires

[signalpoint]

Reported by: http://drupal.org/user/634952 (zhongguo999999)

You cannot quit (logout) if a session expires.

Reproduce the Bug：

1. I manually deleted the session in the sessions table by openning phpmyadmin;
2. Then I click the logout button on my android phone app;
3. I cannot quit. You always receive several errors like this, "User is not logged in." or "Not Acceptable: User is not logged in." etc.

[scotthooker]

Equally if I manually delete my session (which I was testing as I haven't made my logout page yet!) then drupalgap still things I'm logged in.