smtp-auth-plain: Handle multiline SMTP greetings
smtp-auth-plain: Handle multiline SMTP greetings

Fixes: https://bugzilla.gnome.org/702263

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