The event signals that the mouse has left the window.
This happens also when a popup is shown (overlapping the original window).
Before a mouse area would still think it was in pressed state
when the popup (QWindow/QMenu) was shown and even after the popup was closed.

Change-Id: I6d32571f5a473610f60e9476850989ff665edb93
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>