Issue #3483: parent_id not always available as index

[herbdool]

Fixes https://lab.civicrm.org/dev/core/-/issues/3483

Overview

Don't need parent_id when deleting a note, even if it's a child note aka "comment". In fact, it's not even available. So check if it is empty or not.

[civibot]

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[colemanw]

Merging this is a no-brainer, even though it doesn't solve every problem in that entity, it solves one of them!