QmlDesigner: Fix 'jumping around' when moving items in the Visual Editor

This regression was caused by Qt change
6f88388db4e8e2, which disabled the automatic setting of QObject::parent

Reviewed-by: Marco Bubke

src/plugins/qmldesigner/core/instances/nodeinstance.cpp

@@ -261,7 +261,7 @@ NodeInstance NodeInstance::parent() const
 
 bool NodeInstance::hasParent() const
 {
-    return m_nodeInstance->object()->parent();
+    return m_nodeInstance->parent();
 }
 
 /*!