This addresses an inconsistency where 0 could mean one of the three scenarios:
* Invalid comment ID.
* Invalid comment post ID.
* No DB rows updated. This is not an error and should not be treated as one.
With this change, `wp_update_comment()` always returns either `false` or a `WP_Error` object on failure, depending on the value of the `$wp_error` parameter.
Follow-up to [48154], [48215], [48216], [48218], [48230].
Props dd32, jnylen0, enrico.sorcinelli.
Fixes#39732. See #38700, #39735.
git-svn-id: https://develop.svn.wordpress.org/trunk@48235 602fd350-edb4-49c9-b593-d223f7449a82
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