Make sure user ID exists

[andrewlimaza]

• BUG FIX: Fixes an issue where "Recent Members" dashboard widget would throw a warning for a recently deleted user as the code is cached and not cleared on user deletion.

This adds a final check before outputting the data to ensure that the user exists.

Another option would be to cache this for a shorter period in time or clear cache on user deletion.

All Submissions:

• Have you followed the Contributing guideline?
• 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?

How to test the changes in this Pull Request:

1. Ensure WP_DEBUG is enabled.
2. Delete a member from the Users Table (but it has to be a recent member)
3. Navigate to the dashboard widget "Recent Members" and see the error.
4. Implement this code
5. Re-view the Recent Member widget and see the user is gone. This is same functionality as once the transient is cleared.

See ticket #562793 for reference.

Other information:

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

Changelog entry

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

[dparker1005]

With this solution, deleted users may cause fewer than 5 members to be shown in the dashboard report. In the worst case, if all of the 5 most recent members were deleted, an empty table would be shown.

Would we want to consider an alternative approach where we could build the array of WP_User objects immediately after the line $theusers = get_transient( 'pmpro_dashboard_report_recent_members' );, and if any of those user objects does not exist, "break" the transient and get fresh data via SQL?

[andrewlimaza]

I think that could work too, this was a solution for until the transient expires but I could see it going that way (or just caching it for a shorter period like 1 hour? which would reduce the chance of this happening.

Another solution would be to delete the transient on any user deletion?

[dparker1005]

The more I think about this, the more I am on board with this quick fix. You're right, the transient will expire and then everything will be good. This PR avoids PHP errors/warnings, so is a huge improvement over the code already there. I like it