Fix potential vulnerable cloned function

[npt-1707]

Dear Development team,

I identified another vulnerability in a clone function convert_to_decimal() in extern/hunspell/intl/vasnprintf.c sourced from coreutils/gnulib. These issues, originally reported in CVE-2018-17942, were resolved in the gnulib repository via this commit https://github.com/coreutils/gnulib/commit/278b4175c9d7dd47c1a3071554aac02add3b3c35.

This PR applies the corresponding patch to fix the potential heap memory overrun in this codebase.

Please review at your convenience. Thank you for your time and attention!