Bug 1096824 - [Loop] Sign up requests might be unauthorized due to assertions expired

See bug https://bugzilla.mozilla.org/show_bug.cgi?id=1096824. Action happens at https://github.com/jaoo/firefoxos-loop-client/tree/1096824.
https://github.com/mozilla-b2g/firefoxos-loop-client/blob/master/app/js/helpers/account_helper.js#L230

I was referring to this signIn. If onlogin fires (which will do when watch is called with the user logged in) and the idflow is *not* running, and the user is the same we already have then we won't do a signUp but a signIn. And in that case, unless I'm missing something, if the authentication fails we just fire an onlogin error without any check