Reader: Fix viewDidDisappear crash

[momo-ozawa]

Fixes #20843

Description

• Fixes a crash that happens when closing the Reader

How to test

1. Switch to the Reader tab
2. Tap on a Reader post to open the details screen
3. Go back to the Reader feed
4. Repeat steps 2, 3 several times
5. ✅ Verify: the app doesn't crash

Regression Notes

1. Potential unintended areas of impact
   n/a

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   n/a

3. What automated tests I added (or what prevented me from doing so)
   n/a

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

	Warnings
⚠️	This PR is assigned to a milestone which is closing in less than 4 days Please, make sure to get it merged by then or assign it to a later expiring milestone

Generated by 🚫 dangerJS

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Alpha by scanning the QR code below to install the corresponding build.

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr20844-291a5de
	Version	22.6
	Bundle ID	org.wordpress.alpha
	Commit	291a5de
	App Center Build	WPiOS - One-Offs #5971

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Alpha by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr20844-291a5de
	Version	22.6
	Bundle ID	com.jetpack.alpha
	Commit	291a5de
	App Center Build	jetpack-installable-builds #4999

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[hassaanelgarem]

LGTM 🚀

[momo-ozawa]

FYI @mokagio 🙇‍♀️