Fixed bug in Move() related to updating AttributeDescriptors

When moving a `ContentTypeDescriptor` to a different parent, the `ContentTypeDescriptor.AttributeDescriptors` collections of each descendant `ContentTypeDescriptor` must be updated, since those will contain cached references to `AttributeDescriptor`s inherited from their parents.

While this code was in place, it compared the `topic.Parent` to the `target` (parent) _after_ `topic` had _already_ been moved to `target`. As such, this code would never fire, because it would never appear as though the `ContentTypeDescriptor` was being moved to a _new_ parent. Oops.

This fixes this by storing a reference to the previous parent, and then comparing that to the target after calling `SetParent()`.

Author: JeremyCaney

OnTopic/Repositories/TopicRepositoryBase.cs

@@ -434,6 +434,7 @@ public virtual void Move([ValidatedNotNull, NotNull]Topic topic, [ValidatedNotNu
       /*------------------------------------------------------------------------------------------------------------------------
       | Perform base logic
       \-----------------------------------------------------------------------------------------------------------------------*/
+      var previousParent        = topic.Parent;
       MoveEvent?.Invoke(this, new MoveEventArgs(topic, target));
       topic.SetParent(target, sibling);
 
@@ -444,7 +445,7 @@ public virtual void Move([ValidatedNotNull, NotNull]Topic topic, [ValidatedNotNu
       | collection. As such, when a content type is moved to a new location, the attribute descriptors for itself and all
       | descendants needs to be reset to ensure the inheritance structure is updated.
       \-----------------------------------------------------------------------------------------------------------------------*/
-      if (topic.Parent != target && topic is ContentTypeDescriptor) {
+      if (previousParent != target && topic is ContentTypeDescriptor) {
         ResetAttributeDescriptors(topic);
       }