exchange: Fix the error propagation in refresh_account
exchange: Fix the error propagation in refresh_account

... and make it consistent with add_account.

Fixes: https://bugzilla.gnome.org/689642

felipeborges/gnome-online-accounts,ritzk/gnome-online-accounts,ritzk/gnome-online-accounts,felipeborges/gnome-online-accounts,Distrotech/gnome-online-accounts,halfline/gnome-online-accounts,Distrotech/gnome-online-accounts,halfline/gnome-online-accounts,dnohales/gnome-online-accounts,ritzk/gnome-online-accounts,dnohales/gnome-online-accounts,Distrotech/gnome-online-accounts,halfline/gnome-online-accounts,felipeborges/gnome-online-accounts,dnohales/gnome-online-accounts