change workspace hidden eventing

Author: zavub

src/DynamoCore/Models/DynamoModel.cs

@@ -325,9 +325,8 @@ public WorkspaceModel CurrentWorkspace
             set
             {
                 if (Equals(value, currentWorkspace)) return;
-                var old = currentWorkspace;
+                OnWorkspaceHidden(currentWorkspace);
                 currentWorkspace = value;
-                OnWorkspaceHidden(old);
                 OnPropertyChanged(nameof(CurrentWorkspace));
             }
         }