We simply ignore such instructions. This is invalid, but it doesn't
harm; and indeed, there exist such subsetted fonts in PDFs.
Reported by Albert Astals Cid <aacid@kde.org>.
* src/cff/cffgload.c (cff_decoder_parse_charstrings)
[cff_op_hlineto]: Ignore instruction if there aren't any arguments
on the stack.