[auth] call onError if user token already exists instead of return

[Shahidh K Muhammed]

[Tanmai Gopal]

@shahidhk Can you elaborate?

[Shahidh K Muhammed]

at line 17 of Auth.js,

 if (this.hasura.user.token) {
      logError('A user session already exists. Use this.hasura.logout() first?');
      return;
}

If someone tried to login again, even if an onError callback is passed, it is not called. Hence this error cannot be captured from the client code.

Client can check for existing sessions before showing the login screen, but onError callback should be able to catch these errors.

[Tanmai Gopal]

Fixed in v0.1.3