metadata-indexer: open graph images may have CORS rules or be broken links

[davidfurlong]

Embeds may have metadata that has a broken link, we should make the Mods that render them fail more gracefully and not render a broken image square. An example is warpcast links which use a private og:image, perhaps to prevent sites like twitter from rendering the cast preview

[davidfurlong]

Fix is here: https://warpcast.com/df/0xf692e73b