Drag&Drop does not work for leaf nodes after collapsing and uncollapsing

[danielcaldas]

Describe the bug
When the config collapsible is set to true, left nodes that have once been collapsed cannot be dragged anymore, instead the whole graph will be dragged in the attempt of dragging that specific node.

To Reproduce
Steps to reproduce the behavior:

1. Go to the sandbox
2. Click on the checkbox of collapsible
3. Click on some node to collapse a leaf node
4. Click again on the same node to make the previously hidden leaf node visible
5. Try to drag and drop that leaf node, it won't work. Instead the whole graph will be dragged

Expected behavior
Users should be able to drag&drop visible nodes individually.

Environment:
All. Not environment-specific.