textproc/md4c: update to 0.5.2

ChangeLog: https://github.com/mity/md4c/blob/master/CHANGELOG.md

Fixes CVE-2021-30027: DoS with malformed Markdown.

• Base Score: 5.5 MEDIUM
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

PR: 280956
Reported by: alster@vinterdalen.se
MFH: 2024Q3 (security fix)
Security: CVE-2021-30027

(cherry picked from commit 156b0ec23240ad23d3786eabf689799c9d919bac)