Fix for case where the post meta sale ID isn't actually a sale CPT

[kimcoleman]

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Changes proposed in this Pull Request:

We had a weird edge case where the post had a custom field for sale ID that wasn't actually a SWS CPT, so it was still wrapping the content of the page in the swsales divs. This change fixes that case by first validating that the returned sale is a SWS sale.

Other information:

• [x] Have you added an explanation of what your changes do and why you'd like us to include them?
• [x] Have you successfully run tests with your changes locally?

Changelog entry

• BUG FIX: Fixed edge case where a post meta field for sale ID was not a SWS CPT.

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.