[platforms/x11-windows] Delay x11 event processing till Workspace is started

If the event processing is started before everything is fully started
it can happen that we have "evil" events which may crash either Xwayland
or KWin itself. E.g. if the nested window is too large, the window
manager on the host X-Server will request a resize. If the backend does
that it can happen that the wl_output gets destroyed while Xwayland tries
to bind to it and will crash. Thus let's delay all events till we are
ready to process them.

plugins/platforms/x11/windowed/x11windowed_backend.cpp

@@ -92,7 +92,7 @@ void X11WindowedBackend::init()
         }
         XRenderUtils::init(m_connection, m_screen->root);
         createWindow();
-        startEventReading();
+        connect(kwinApp(), &Application::workspaceCreated, this, &X11WindowedBackend::startEventReading);
         connect(this, &X11WindowedBackend::cursorChanged, this,
             [this] {
                 createCursor(softwareCursor(), softwareCursorHotspot());