Fix NPE on History List screen

[aditi-bhatia]

Fixes #20808

This PR adds null checks to HistoryDetailContainerFragment.java to address a NPE crash in mapRevisionModelsToRevisions(). I have been unable to reproduce the crash myself but it occurs when current is null in revisions.add(new Revision(current)) (line 195).

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To Test:

1. Smoke test this screen: My Site -> Pages -> Click on a page -> Meatball menu -> History -> Click on a revision

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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)

   • None

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

   • None

PR Submission Checklist:

• [x] I have completed the Regression Notes.
• [x] I have considered adding accessibility improvements for my changes.
• [x] 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)~

[sonarcloud[bot]]

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

[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	pr20816-31615f5
	Commit	31615f53b4368d69ef331e561d82233d3edbd136
	Direct Download	jetpack-prototype-build-pr20816-31615f5.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	pr20816-31615f5
	Commit	31615f53b4368d69ef331e561d82233d3edbd136
	Direct Download	wordpress-prototype-build-pr20816-31615f5.apk

Note: Google Login is not supported on these builds.