Fan speed status stuck at last non-zero value when fan drops to 0 RPM

[Chow Loong Jin]

On the System76 Lemur Pro, the fan rgularly turns off at lower temperatures (anything below 60°C), and `sensors` reports 0 RPM.

When this happens, the fan speed status in tmux gets stuck at the last non-zero value. Looking in /dev/shm/byobu-*-*/status.tmux/, I see a `fan_speed` file that says 3161 RPM and a `fan_speed.new` file that is empty.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: byobu 5.133-0ubuntu1
Uname: Linux 5.7.6-hyper1+ x86_64
ApportVersion: 2.20.11-0ubuntu27.9
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: GNOME
Date: Mon Sep 28 17:28:36 2020
PackageArchitecture: all
SourcePackage: byobu
UpgradeStatus: Upgraded to focal on 2020-05-21 (129 days ago)
modified.conffile..etc.default.apport: [modified]
modified.conffile..etc.profile.d.Z97-byobu.sh: [deleted]
mtime.conffile..etc.default.apport: 2014-07-23T09:56:20.981816