generate only future dates and only if is_on_sale is true

[masteradhoc]

All Submissions:

• Have you followed the Contributing guidelines?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

"date_on_sale" shouldnt generate past dates and only generate if the product is actually on sale (sale price is set)

Closes #171.

How to test the changes in this Pull Request:

1. apply the pr
2. generate some products
3. check if for not on sale products the sale to date is set - if not good
4. check if for on sale product the sale to date is in the future - if yes good

Screenshots

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?

Changelog entry

Make sure "date_sale_to" only generate future dates
Make sure "date_sale_to" is only set if the product is on sale

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

FOR PR REVIEWER ONLY:

• I have reviewed that everything is sanitized/escaped appropriately for any SQL or XSS injection possibilities. I made sure Linting is not ignored or disabled.