if i call something like
Plasma::WindowEffects::slideWindow(m_view->winId(), Plasma::BottomEdge, 0);

i expect the window sliding in and out from the bottom edge of the screen, even if the window is not physically attached to the screen bottom edge.

right now it only produces garbage on the screen (some frames of the animation that don't get cleared out)
this patch makes it work, maintaining the same behavior for existing popups