Input unresponsive after screen blank since 209b1ba3

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=974172

We've had a bug report in Debian that after upgrading mutter from 3.38.0 to 3.38.1 on multiple arm64 (aarch64) systems, the keyboard and mouse become unresponsive and GNOME Shell cannot be unlocked.

One user reports that "The screen can be unlocked if it is not blanked, but it cannot be unlocked after blanking".

Apparently this regressed with 209b1ba3 "clutter/frame-clock: Adapt refresh rate from to frame info".

Perhaps the frame rate needs a minimum, so that even if no frames are drawn at all, the frame-clock still runs?