Cocoa integration - suppress excessive dragginUpdated messages

Our abstract item views are using a timer before starting autoscroll.
Constant dragginUpdated (re)starts this timer again and again and it
actually never times out (== no autoscroll). It looks like  a bug in Cocoa since 10.11,
they test: respondsToSelector:@selector(wantsPeriodicDraggingUpdated:) with
':' at the end, though they need a method without parameters; as a result
QTBUG-32761 was re-introduced.

Let's make them happy and respond to this selector also (never gets called
actually).

Change-Id: I3b7bb0a455124f84c97fc350f69486bf0fc5d5fc
Task-number: QTBUG-32761
Reviewed-by: Jake Petroules <jake.petroules@theqtcompany.com>

src/plugins/platforms/cocoa/qnsview.mm

@@ -1898,6 +1898,18 @@ static QPoint mapWindowCoordinates(QWindow *source, QWindow *target, QPoint poin
     return NO;
 }
 
+
+- (BOOL)wantsPeriodicDraggingUpdates:(void *)dummy
+{
+    // This method never gets called. It's a workaround for Apple's
+    // bug: they first respondsToSelector : @selector(wantsPeriodicDraggingUpdates:)
+    // (note ':') and then call -wantsPeriodicDraggingUpdate (without colon).
+    // So, let's make them happy.
+    Q_UNUSED(dummy);
+
+    return NO;
+}
+
 - (void)updateCursorFromDragResponse:(QPlatformDragQtResponse)response drag:(QCocoaDrag *)drag
 {
     const QPixmap pixmapCursor = drag->currentDrag()->dragCursor(response.acceptedAction());