Revert logic change in Class.SetProperty

Logic is invalid and causes errors when a symbol has previously been set, especially when set to null

UIX/Microsoft/Iris/UI/Class.cs

@@ -112,11 +112,9 @@ namespace Microsoft.Iris.UI
 
         public virtual void SetProperty(string name, object value)
         {
-            if (_storage.ContainsKey(name))
+            if (_storage.ContainsKey(name) && Utility.IsEqual(_storage[name], value))
                 return;
             _storage[name] = value;
-
-            if (Utility.IsEqual(_storage[name], value))
             _notifier.Fire(name);
         }