Fix a crash on x11 on closing laptop lid

On x11 when multiscreen is enabled often kwin crashes on
laptop lid close, for two reasons:
* m_outputLayer going dangling in RenderLayer: fixed by using a QPointer
* m_activeOutput going dangling in Workspace

For the latter, the output disabling was done correctly, but x11client did set the old deleted output
again in X11Client::moveResizeInternal
This is fixed by moving desktopResized() at the bottom of
Workspace::slotOutputDisabled() after the reassign of outputs to
the toplevels