kerberos: Zero initialize operation structure
kerberos: Zero initialize operation structure

We need zero initialize the structure so we don't end up
freeing unused members when cleaning up the operation.

https://bugzilla.gnome.org/show_bug.cgi?id=739593

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