Fix a crash that occurs when remove a user

[irfano]

This fixes some parts of #20535.

The crash message is Can not perform this action after onSaveInstanceState.

This PR adds a check for the fragment's state and doesn't run the fragmentManager.popBackStack(); if the fragment's state is saved.

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To Test:

1. Log in.
2. Tap more button on "My Site".
3. Tap People.
4. Tap a user item.
5. Tap the trash icon at the top right to remove the user.
6. Tap the REMOVE button on the dialog but go to device home immediately after tapping the REMOVE button.
7. on trunk this should cause a crash with Can not perform this action after onSaveInstanceState message. Ensure it doesn't crash on this PR.

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Regression Notes

1. Potential unintended areas of impact

   • None

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)

   • This is a very hard case to reproduce. Not a proper case for UI tests.

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PR Submission Checklist:

• I have completed the Regression Notes.
• 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.

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Testing Checklist (strike-out the not-applying and unnecessary ones):

• WordPress.com sites and self-hosted Jetpack sites.
• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• Talkback.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• Large and small screen sizes. (Tablet and smaller phones)
• Multi-tasking: Split screen and Pop-up view. (Android 10 or higher)

[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
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr20837-69a8ccc
	Commit	69a8ccc
	Direct Download	jetpack-prototype-build-pr20837-69a8ccc.apk

Note: Google Login is not supported on these builds.

[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
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr20837-69a8ccc
	Commit	69a8ccc
	Direct Download	wordpress-prototype-build-pr20837-69a8ccc.apk

Note: Google Login is not supported on these builds.

[aditi-bhatia]

I was able to reproduce the crash on trunk and the fix works as expected 👍

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud