Extract ODs from parent comment

[Chaphasilor]

If an invoking comment is not a top-level comment, first check if there are any OD URLs in the parent comment (the one to which the invoking comment replies to) and only scan the post if there aren't any.

Depending on how this is implemented in snoowrap, it might be as simple as always checking the parent (if a top-level comment's parent is the post itself)...