Comments: Make `wp_update_comment()` return a `WP_Error` object on database...

Comments: Make `wp_update_comment()` return a `WP_Error` object on database error, if `$wp_error` parameter is true.

Follow-up to [48154], [48215].

See #39732.
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git-svn-id: https://core.svn.wordpress.org/trunk@47985 1a063a9b-81f0-0310-95a4-ce76da25c4cd