[imgbox] Direct image links don't trigger the imgbox extractor

[taskhawk]

Came across this post with direct image links from imgbox but they trigger the generic directlink extractor instead of the imgbox's.

https://www.bellazon.com/main/topic/56-candids/page/514/#comment-4163878

I get why, and not a big deal but the imgbox extractor makes available the image_key key in the metadata, useful as a unique short id, while directlink can't offer something similar and filename isn't as useful as that could be anything depending on source (though if I wanted to, I could probably work something with a postprocessor). I use them like this in my config, for example:

    "bellazon>directlink": {
      "filename": "{bellazon[post][id]}-{bellazon[num]:>02}.{extension}"
    },
    "bellazon>imgbox": {
      "filename": "{bellazon[post][id]}-{bellazon[num]:>02}-{image_key}.{extension}"
    },
    "bellazon>imgur": {
      "filename": "{bellazon[post][id]}-{bellazon[num]:>02}-{id}.{extension}"
    },
    "bellazon>imxto": {
      "filename": "{bellazon[post][id]}-{bellazon[num]:>02}-{token}.{extension}"
    }