`media_handle_sideload()` may unexpectedly return 0 on error

[jirihon]

This is closely related to #41726. The documentation of media_handle_sideload() (same as for media_handle_upload()) states that it will always return the attachment ID on success, or a WP_Error object on failure. However, it currently may return 0 as well if something fails with the attachment post insertion. That is because wp_insert_attachment() and wp_insert_post() do not return WP_Error objects by default, and media_handle_sideload() for some reason does not change this like it should.

This requires a simple fix: call wp_insert_attachment() with the fourth parameter set to true as it was recently fixed for the media_handle_upload() in #41726.

[subrataemfluence]

Proposed patch

[joemcgill]

Thanks for the writeup, @jirihon and for the patch, @subrataemfluence. It looks good to me.

One quick note on ticket process, the version property on a ticket is meant to refer to the version of WordPress where a bug was introduced and/or the earliest version where you can reproduce this bug. I don't really see a need to go back through WP history to identify that moment in this instance.

Cheers!

[pento]

In 44634:

Media: media_handle_sideload() expectes wp_insert_attachment() to return a WP_Error.

For wp_insert_attachment() to do that, we need to be setting the $wp_error parameter to true.

Props subrataemfluence, jirihon.
Fixes #44303.