Check we have matched a preview URL by ID when exiting preview

[AndyButland]

Prerequisites

• I have added steps to test this contribution in the description below

Description

I found this issue when testing the 13.8 RC. It's not a regression introduced in 13.8 as far as I can tell, but still something we could fix up.

You can reproduce by:

• Open up a page on the front-end website.
• In another tab, open the backoffice, edit that page and click "Save and Preview"
• Refresh the first page and you'll see the "View published version?" dialog
• Click "View Published Version" and that would lead to an error as we attempt to parse a non-integer value as an integer.

With the PR in place this will no longer error.

[Copilot]

Pull Request Overview

This PR addresses an error when parsing a preview URL by ensuring that the ID extracted from the URL is a valid integer before using it.

• Added a guard using int.TryParse to safely parse the preview ID.
• Removed the redundant int.Parse call after the validation.

[AndyButland]

Cherry-picked into release/13.8.0,