Temporary fix for corrupted characters
Fixes Issue #3374 (closed), by falling back on the deprecated in-python fonttools based technique for doing subsetting. To be removed once the new MuPDF-based code is a little more mature, or at least once [1, 2] are fixed.
[1] https://github.com/pymupdf/PyMuPDF/issues/3470 [2] https://github.com/pymupdf/PyMuPDF/issues/3494