(Some) imgur images are failing to upload with 422: Unprocessable Entity

[BooDoo]

[https://docs.joinmastodon.org/methods/media/#422-unprocessable-entity](422: Unprocessable Entity) for imgur-hosted images. Not all of them, but often. Including images that have previously posted successfully, and which appropriately use the i.imgur.com subdomain.

Seems to be related to changes in imgur's service, not CBTS, but it would be good to fix if possible.

[BooDoo]

leads to recurse_rety cap and failures in backend; fails silently for send_status if the image is posted as an attachment, or results in the blurry "no image resource" icon when the img is composited in an SVG.