Manifest path fix

[jgw96]

fixes #4157

PR Type

Bugfix

Describe the current behavior?

As the user showed in the issue, it is possible to get into a state where getManifest returns nothing, which would cause the generated manifest to not be linked to the index.html.

Describe the new behavior?

We now pass the manifestPath directly as a "backup" value, which would avoid any, unlikely, breakage as it is just a backup value to how things normally work.

PR Checklist

• [x ] Test: run npm run test and ensure that all tests pass
• Target main branch (or an appropriate release branch if appropriate for a bug fix)
• [x ] Ensure that your contribution follows standard accessibility guidelines. Use tools like https://webhint.io/ to validate your changes.

Additional Information

[microsoft-github-policy-service]

Thanks jgw96 for opening a Pull Request! The reviewers will test the PR and highlight if there is any conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌

[github-actions]

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