Invoice template function uses domain id instead of contact id to get address parts

Tax invoice generation uses the wrong key from the domain structure to get the address parts.

The effect is subtle - invisible if the domain contact id is the same as the domain id, which is usually the case for the initial domain (id 1, contact_id 1), but not if a multisite domain has domains added later, and sometimes not for the initial domain (this is how I stumbled upon the bug, however I don't know how to reproduce these conditions).

One line fix, attached.