manage mouse events when out of the window

mouseareas must support event grabbing when the mouse is out of the window too
BUG:377545

shell/panelview.cpp

@@ -761,8 +761,8 @@ bool PanelView::event(QEvent *e)
                     return true;
                 }
             } else {
-                // discard event if current mouse position is outside the panel
-                return true;
+                // default handling if current mouse position is outside the panel
+                return ContainmentView::event(e);
             }
             break;
         }