Ensure the panel's view position in the screen

Otherwise resize gets called and xcb moves it to the screen that contains
QPoint(0, 0)

shell/panelview.cpp

@@ -60,6 +60,7 @@ PanelView::PanelView(ShellCorona *corona, QScreen *targetScreen, QWindow *parent
        m_background(0)
 {
     if (targetScreen) {
+        setPosition(targetScreen->geometry().topLeft());
         setScreen(targetScreen);
     }
     setResizeMode(QQuickView::SizeRootObjectToView);