Fix creation of covers for ActivityPub imports

[dato]

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Imports for other BookWyrm instances were showing without covers for me, and I think this is the cause?

Code seemed correct, as in, I thought value here would be a document. But then the comment refers to receiving JSON, in which case the code is not correct. For this reason I've left both.

[prolibre]

Oh great! Thank you so much !

[hughrun]

I can check this tomorrow.

The comment is confusing, because it refers to a "JSON blob" which initially made me think it meant a Blob.

value here is only the image field listed within the ActivityPub JSON for a given activity. It's called from set_field_from_activity.

I think what the comment is meant to convey is that sometimes value is just the url as a string (if it's pulled from an "attached" image), and sometimes it's originally a JavaScript object (if the image is in intrinsic part of the ActivityPub object, as in the case of a user or Edition).

[mouse-reeve]

This seems like it works to me -- is there any reason it's still a draft?

I believe I meant that the value can either be a dict or a string, but I wrote it to support objects, possibly because the activitypub could be passed in still as an ActivityPub object, even though evidently it's coming in as a dict