readMetadata returns empty metadata when the trailer has no /Info, ignoring XMP and /Lang #1694

readMetadata in packages/pdf-codec/src/read.ts returns {} as soon as the trailer has no /Info dictionary, before it looks at the catalog's /Lang or the XMP packet. A PDF with no /Info but with an XMP packet (the usual PDF/A shape) therefore reports empty metadata, even though the comment a few lines further down says the fields "live only in XMP" in such files, and the surfaces docs and README say metadata "still reads the XMP packet".

Repro: write a PDF whose trailer has no /Info, whose catalog has /Metadata pointing at an XMP stream carrying dc:title and dc:creator, and a /Lang entry. readPdf returns metadata: {} where the title, author and language are all present in the file.

Found while reviewing #1693; not caused by it.