QCocoaDrag: Only update m_lastView when it actually changes

The underlying QObjCWeakPointer used to track the view requires
a bit of bookkeeping, so avoid updating its value unless the
view actually changes.

Pick-to: 6.8 6.9
Change-Id: I6a1aeaf0e6e0eb221d55de00c8f30259832e58fa
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/plugins/platforms/cocoa/qcocoadrag.mm

@@ -35,7 +35,8 @@ void QCocoaDrag::setLastInputEvent(NSEvent *event, NSView *view)
 {
     [m_lastEvent release];
     m_lastEvent = [event copy];
-    m_lastView = view;
+    if (view != m_lastView)
+        m_lastView = view;
 }
 
 QMimeData *QCocoaDrag::dragMimeData()