Log Message:
Markdown: apply Debian patch to exit gracefully if input cannot be opened

https://metadata.ftp-master.debian.org/changelogs//main/m/markdown/markdown_1.0.1-10_changelog

  markdown (1.0.1-10) unstable; urgency=medium

    * Exit with a non-zero exit code if the input file cannot be opened,
      thanks to Chris Lamb, closes: #886032.