QGestureManager: use gesture owner target if topLevelAt returns nullptr

For security reason, Wayland doesn't provide global position for
top level windows, so topLevelAt is not supported.

Fixes: QTBUG-113404
Pick-to: 6.5 6.2 5.15
Change-Id: Id60b8b77a1843344db4d4e4c13382ad87adac806
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit 10c3dd87d3bc2e84d4f477888622f5fc7ed5d502)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/kernel/qgesturemanager.cpp

@@ -610,7 +610,8 @@ void QGestureManager::deliverEvents(const QSet<QGesture *> &gestures,
                     QWidget *child = topLevel->childAt(topLevel->mapFromGlobal(pt));
                     target = child ? child : topLevel;
                 }
-            } else {
+            }
+            if (!target) {
                 // or use the context of the gesture
                 QObject *context = m_gestureOwners.value(gesture, 0);
                 if (context->isWidgetType())