A4A: Make sure we aren't trying to use an undefined plan

[travisw]

Related to #

Proposed Changes

• Check for undefined before trying to use a plan.

Why are these changes being made?

• This keeps the frontend from breaking when we ship new Pressable plans on the backend that haven't been added to the frontend yet.

Testing Instructions

• Make sure the Pressable marketplace page (/marketplace/hosting/pressable) works exactly the same as before. There aren't any functional changes.
• Sandbox public-api.wordpress.com
• Apply D166722-code on the backend.
• Test again and make sure everything still works as expected.
• To be extra sure, make sure the wpcom hosting page works fine as well.

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[bot]]

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[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~12 bytes added 📈 [gzipped])

``` name parsed_size gzip_size a8c-for-agencies-marketplace +48 B (+0.0%) +12 B (+0.0%) ``` Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

**Parsed Size:** Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory. **Gzip Size:** Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.