textproc/htmldoc: update to 1.9.16

ChangeLog: https://www.msweet.org/blog/2022-05-19-htmldoc-1.9.16.html

Submitter becomes new maintainer. Current maintainer has been
inactive/unresponsive for a long time.

PR: 264183
Reported by: fuz@fuz.su
Approved by: jose@diasfernandes.pt (maintainer, timeout 2 weeks)
MFH: 2022Q2 (bugfixes)