Fixed graph edits transfering into history

src/editor/editor.tsx

@@ -439,7 +439,7 @@ export class Editor extends React.PureComponent<any, stateTypes> {
 
     private loadGraphFromCheckpoint(checkpoint: Checkpoint<SimGraphData>) {
         const graph = new DynamicGraph();
-        graph.fromSerializedObject(checkpoint.data);
+        graph.fromSerializedObject(JSON.parse(JSON.stringify(checkpoint.data)));
 
         // Transfer checkpoints to new graph object
         graph.history.copyCheckpointsFromHistory(this.state.graph.history);