wp_notify_moderator assumes the post_author userdata exists

[rachelbaker]

When attempting to notify the moderator about a new comment that is awaiting approval, the $post->post_author userdata is assumed to exist. Which means if the $post->post_author === 0 the userdata ($user->ID) does not exist and results in a "Trying to get property of non-object" PHP notice.

https://core.trac.wordpress.org/browser/trunk/src/wp-includes/pluggable.php#L1550

The (deprecated) function wp_notify_postauthor did/does confirm that the $post->post_author userdata exists before using it.

[Oxymoron]

Attached a patch. I believe it solves the problem in question. The main thing I am worried about it the amount of if() statements being nested. Let me know if that's an issue or if there is an issue with the patch in general and I will fix.

[Oxymoron]

Updated patch to better address the issue the ticket reports. Thanks to Rachel for going over the problems with my initial patch via Slack.

[boonebgorges]

In 32692:

In wp_notify_moderator(), don't throw notice when comment belongs to a post with no author.

Props Oxymoron.
Fixes #32566.