Domains: Fix WSOD during domain checkout

[rafaelgallani]

Fixes #97024.

Proposed Changes

Fixes a WSOD introduced indirectly in #96568 - domain can possibly be undefined, but this isn't accounted for since its type definition is invalid - we should fix this in the future, but for now, this PR only fixes the WSOD on it, by adding optional chaining so we can prevent undefined value checks.

Why are these changes being made?

A WSOD can happen during the post-checkout ("thank you") page for a domain.

Testing Instructions

Same as #97024:

• Checkout and build this branch locally or access its calypso.live link;
• Visit https://wordpress.com/domains/add/ and select a site you own;
• Select a domain to purchase;
• Continue to checkout;
• Complete checkout;
• Ensure you don't get a WSOD when completing checkout - as opposed to what's currently happening in production.

Preview

Before	After

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-126354

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-126354&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-126354&env=a8c-for-agencies

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug fix/wsod-domains-thank-you-page on your sandbox.

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[gius80]

LGTM