sed: The change ("c") command should start a new cycle.

The "c" command should start the next cycle as clarified in POSIX 2024.
This is also consistent with historical and gnu sed behavior.

This patch is from OpenBSD by way of NetBSD with a tweak to the man page
date by me.

Confirmed the test case in the bug now works.

PR: 271817
Obtained from: NetBSD (1.39 uwe), OpenBSD (1.39 millert)
Sponsored by: Netflix