getOfferResult() call missing from zoe offer example

[dckc]

In Trading with Offer Safety we have:

const seat = E(zoe).offer(toJoin, proposal, { Price });
const places = await E(seat).getPayout('Places');

but we're missing a call to E(seat).getOfferResult().

see also

• https://github.com/Agoric/agoric-sdk/issues/8939