If Xwayland has crashed, the Workspace will block stacking order updates
and start destroying all X11 clients.
Once stacking order updates are unblocked, the Workspace will mark the X
stacking order as dirty and create a new Xcb::Tree object.
We don't want to create that Xcb::Tree object because accessing it
after the XCB connection has been shut down will lead to a crash.
BUG: 427688
FIXED-IN: 5.20.1
If the Xwayland process has crashed due to some bug, the user should
still be able to start applications in Xwayland mode. There is no reason
to restart the whole session just to be able to launch some application
that doesn't have native support for Wayland.
