Prevent crashes when retained posts are deleted

[crazytonyli]

The app may crash when delete/trash an post that's already deleted on the server but yet to be synced.

Here is the easiest way to reproduce the crash. It may not exactly match what's happening to the real users, but the root cause is the same:

1. Simulate a slow network, go to the app's posts list. The posts are being refreshed in the background, slowly.
2. Tap more actions on a post, and select Trash. You'll see an alert. Leave the alert on.
3. On the web, delete the selected post.
4. The app's post list is refreshed.
5. Confirm the trash post alert. App crashes.

Sentry records a new issue for this crash (i.e., https://a8c.sentry.io/issues/7703437016/?project=1438083), but it's not actually new (i.e., https://a8c.sentry.io/issues/7398708809/?project=1438083).

[wpmobilebot]

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

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	34454
	Version	PR #26015
	Bundle ID	org.wordpress.alpha
	Commit	fad6452
	Installation URL	1hvhavh9bo048

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

[wpmobilebot]

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

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	34454
	Version	PR #26015
	Bundle ID	com.jetpack.alpha
	Commit	fad6452
	Installation URL	26o1cd6hplolg

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