nz-tree responses to drag events when nzDraggable is set to false

[Fanoid]

Version

1.7.0

Environment

MacOS, Chrome 69

Reproduction link

https://stackblitz.com/edit/angular-kaupwu

Steps to reproduce

1. create a nz-tree components, then use nzTreeTemplate to define tree nodes
2. set nzDraggable to false
3. add draggable="true" to elements in nzTreeTemplate
4. drag one tree node to other parent nodes

What is expected?

nz-tree should not response to other user-defined drag events, as nzDraggable is set to false.

What is actually happening?

The node can be dragged to other places.

Other?

Context: We want to drag tree only leaf nodes to outside of the tree, so we do not use the pre-defined events. But it turns out the tree still make changes when dragging.
Moreover, as our tree data is very large (more than 350 nodes), the process of events causes severe lag for every drag event (~60ms). Especially lots of dragover event are triggered and processed (which is not easy to show in the demo.)