GNOME Shell crashes when deleting workspaces

I could reproduce this using GNOME Tweak Tool: add one ws (-> 5), delete one (-> 4); so far so good. Deleting another one (-> 3) results in the “oh no! something has gone wrong” screen, and the Journal reads:

mutter:ERROR:core/screen.c:1250:update_num_workspaces: assertion failed: (w->windows == NULL)

This looks like https://bugs.debian.org/782075.

Related issues

Related to #11237 (closed)
Has duplicate #11144 (closed)

Original created by @intrigeri on 10797 (Redmine)

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