Mutter crashing when workspace count is changed

[Matt Summers]

Fresh install of Artful nightly from earlier this week.

Steps to reproduce:
1. Open gnome-tweak-tool
2. Browse to workspaces pane
3. Change workspaces count (for me at this time 2->3->2)
4. I am returned to gdm login.

Journal logging (EDIT: shortened as attached anyway):
Aug 17 19:45:31 matt-xps-13-9360 org.gnome.Shell.desktop[1501]: **
Aug 17 19:45:31 matt-xps-13-9360 org.gnome.Shell.desktop[1501]: mutter:ERROR:core/screen.c:1263:update_num_workspaces: assertion failed: (w->windows == NULL)
Aug 17 19:45:31 matt-xps-13-9360 gnome-calendar[2084]: Error reading events from display: Broken pipe
Aug 17 19:45:31 matt-xps-13-9360 gnome-control-c[2077]: Error reading events from display: Broken pipe
Aug 17 19:45:31 matt-xps-13-9360 seahorse[2085]: Error reading events from display: Broken pipe
Aug 17 19:45:31 matt-xps-13-9360 gnome-terminal-[1834]: Error reading events from display: Broken pipe
Aug 17 19:45:31 matt-xps-13-9360 nautilus[2082]: Error reading events from display: Broken pipe
Aug 17 19:45:31 matt-xps-13-9360 gnome-tweak-too[2182]: Error reading events from display: Broken pipe

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: mutter 3.24.3-0ubuntu3
ProcVersionSignature: Ubuntu 4.12.0-11.12-generic 4.12.5
Uname: Linux 4.12.0-11-generic x86_64
ApportVersion: 2.20.6-0ubuntu5
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu Aug 17 19:54:35 2017
EcryptfsInUse: Yes
InstallationDate: Installed on 2017-08-16 (0 days ago)
InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Alpha amd64 (20170815)
SourcePackage: mutter
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Daniel van Vugt (vanvugt)]

Thank you for reporting this bug to Ubuntu.
Ubuntu 17.10 (artful) reached end-of-life on July 19, 2018.

See this document for currently supported Ubuntu releases:
https://wiki.ubuntu.com/Releases

We appreciate that this bug may be old and you might not be interested in discussing it any more. But if you are then please upgrade to the latest Ubuntu version and re-test. If you then find the bug is still present in the newer Ubuntu version, please add a comment here telling us which new version it is in and change the bug status to Confirmed.

[Launchpad Janitor (janitor)]

[Expired for mutter (Ubuntu) because there has been no activity for 60 days.]