Thumbnails are not generated for topics with derive_thumbnail=True when contained content are instances of StudioContentNode

[jamalex]

Observed behavior

When creating a channel using StudioContentNode (which is what is used when creating an automatically-aligned channel), ricecooker doesn't have access to the thumbnails for the content, so it can't auto-create tiled thumbnails for topics that have derive_thumbnail=True.

Expected behavior

I would expect it either to pull the images from Studio to feed into local tile generation, or to generate these thumbnails on the Studio side once uploaded (which would probably be preferable -- could then also have auto-thumbnails applied to channels manually created on Studio.

User-facing consequences

"Ugly folderitis" (aka "fugly folders") on these aligned channels.