A PDF names fonts by PostScript name. When the font isn't installed at import, the importer
splits the name (`Honoka-Mincho` → family Honoka, style Mincho) and the document keeps that
pair. Installing the font later didn't help when its family name shares nothing with its
PostScript name (ほのか明朝): the pair stayed missing. FontDb::canonical now also looks the
pair up, joined, among the PostScript names, and answers with that face's own family and style.