doc: guard against md list parsing edge case

PR-URL: https://github.com/nodejs/node/pull/19647


Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Chen Gang <gangc.cxy@foxmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>