OPDS audiobook manifest order is wrong

[mekarpeles]

Often the Librevox audiobook manifests are missing files from their readingOrder
https://api.archivelab.org/books/kniga_zitij_svjatyh_na_mesjac_avgust_eu_0811_librivox/opds_audio_manifest is totally empty

https://api.archivelab.org/books/short_poetry_087_1004_librivox/opds_audio_manifest ought to have 23 poems as per https://archive.org/details/short_poetry_087_1004_librivox, but it only has one -- the sixth one