loadLazyChildren error

[chengchencc]

Reporting a Bug?

i try to use children lazy load refer to Fix loadLazyChildren with children as function but not work.

i read the source code,find this change in react-sortable-tree.js(row number 150):
` static getDerivedStateFromProps(nextProps, prevState) {
const { instanceProps } = prevState;
const newState = {};

// make sure we have the most recent version of treeData
instanceProps.treeData = nextProps.treeData;
if (!isEqual(instanceProps.treeData, nextProps.treeData)) {
  if (instanceProps.ignoreOneTreeUpdate) {
    instanceProps.ignoreOneTreeUpdate = false;
  } else {
    newState.searchFocusTreeIndex = null;
    ReactSortableTree.loadLazyChildren(nextProps, prevState);
    Object.assign(
      newState,
      ReactSortableTree.search(nextProps, prevState, false, false, false)
    );
  }

instanceProps.treeData = nextProps.treeData;
if (!isEqual(instanceProps.treeData, nextProps.treeData))
`
this will be always equal. the code can not going into the if.

if this change cause bug?

[HgAlexx]

This is related to #369.
I've locally patched this doing a simple backup of instanceProps.treeData before it is overwritten by nextProps.treeData and using the backup for the if (!isEqual(instanceProps.treeData, nextProps.treeData)) { test.
This fix is working fine for me, children are correctly lazyloaded on expanded again.

let prevTreeData = instanceProps.treeData;
// make sure we have the most recent version of treeData 
instanceProps.treeData = nextProps.treeData; 
if (!isEqual(prevTreeData, nextProps.treeData)) {