canDrop() and onMoveNode()'s nextTreeIndex is affected by node collapsing

# How to reproduce

Simple reproduction example (this example simply alerts nextTreeIndex on a drag):
https://2o4p1no0ky.codesandbox.io/

Step 1:
Drag node 1 under node 2. You get an alert "1".

Step 2:
Refresh browser to reset state.

Step 3:
Expand node 2.

Step 4:
Drag node 1 under node 2. You get an alert "3".

Expected behavior: I would always expect nextTreeIndex to be 3, e.g., it should ignore whether nodes are collapsed.