Undo Redo Issue with loading scribble from json

[Sesa1988]

Hi, its a great package but I have some issues with the Undo Redo feature when loading from json:

• Redo deletes the whole painting (can redo is also true before executing the action).
• If I play around with some methods like clearQueue() and set the flag addToUndoHistory to false, it odes not recognise the first line but at least does not remove the whole painting (can redo is also false in this case). Undo does also not work on the first erase on the second case, something seems weird.

In either case I can't make it properly work. Im using flutter_bloc for state and and tried a dirty hack to get the state from the notifier every 100 milliseconds to make sure its not an issue on my side, the behaviour is one of the above described.