Do never return a NULL AgAuthData pointer
Do never return a NULL AgAuthData pointer

Though it might not make much sense to return an AgAuthData when the
method and mechanism are not set, doing so is likely to reduce the code
paths in the caller, which can now always rely on the fact that the
AgAuthData instance will be created.

plotters/accounts-sso.libaccounts-glib,plotters/accounts-sso.libaccounts-glib,plotters/accounts-sso.libaccounts-glib