fd.o #19688: tp_connection_get_contacts_by_id: don't assert if all contacts' IDs are bad
fd.o #19688: tp_connection_get_contacts_by_id: don't assert if all contacts' IDs are bad

tp_connection_get_contact_attributes asserts that there is at least
one handle, so if this is not true, we need to avoid calling it.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib