A library which is purely handwritten doesn't have any paths to generate from, but should still be releasable within Librarian.

Up for debate: should generation skip these, or call the container and let it decide whether or not to do anything. (Inkeeping with #818, I'd argue "the normal generation cycle should skip it, but when updating to a new container we should call it, in case the container generates metadata files etc.)

cc @parthea for input on the questionable bit.

I've assigned this to myself (should be easy enough to fix) and in the first pass I'll make generation skip such libraries.