only call notifyPropertyChanged if actually set to new value

Source/LibationWinForms/grid/AsyncNotifyPropertyChanged.cs

@@ -8,6 +8,8 @@ namespace LibationWinForms
 	{
 		public event PropertyChangedEventHandler PropertyChanged;
 
+		// per standard INotifyPropertyChanged pattern:
+		// https://docs.microsoft.com/en-us/dotnet/desktop/wpf/data/how-to-implement-property-change-notification
 		public void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
 			=> this.UIThreadAsync(() => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName)));
 	}