pixbuf_avatar_from_individual_closure_new: use the g_slice allocator
pixbuf_avatar_from_individual_closure_new: use the g_slice allocator

We are likely to allocate a bunch of those so best to use the g_slice
allocator.

GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets