Reader: Fix post card errors

[tyxla]

Proposed Changes

This PR fixes an error with the reader post card that I found while testing #77046.

I couldn't repro on the reader itself, but since those examples worked at some point, it might indicate a hard-to-repro bug.

Testing Instructions

• Go to /devdocs/blocks/reader-post-card
• Verify you're no longer seeing errors thrown and the reader card loads correctly.
• Go to /devdocs/blocks/reader-combined-card
• Verify you're no longer seeing errors thrown and the reader card loads correctly.

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 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-ajp-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-71673

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-71673&env=jetpack

[matticbot]

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

App Entrypoints (~6 bytes added 📈 [gzipped])

name           parsed_size           gzip_size
entry-stepper        +12 B  (+0.0%)       +6 B  (+0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Sections (~5 bytes added 📈 [gzipped])

name    parsed_size           gzip_size
reader        +12 B  (+0.0%)       +5 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.

Async-loaded Components (~8 bytes added 📈 [gzipped])

name                                                 parsed_size           gzip_size
async-load-design-blocks                                   +15 B  (+0.0%)       +8 B  (+0.0%)
async-load-calypso-components-web-preview-component        +12 B  (+0.0%)       +5 B  (+0.0%)

React components that are loaded lazily, when a certain part of UI is displayed for the first time.

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.

[flootr]

Verified there no errors on this branch 👍🏻