add upstream encoding patch

This is my first salsa PR so hopefully I am doing this right.

I am maintaining the poppler bindings for the R programming language called pdftools. I would like to request a backport of a one-line upstream patch which fixes a really bad encoding bug. Without this patch, the C++ api for extracting text returns corrupted text for anything but plain ascii.

I really hope this can make it into Buster! Thank you for considering.