Upload Dragger component hover bug on borders of inner elements

[guido-visser]

• I have searched the issues of this repository and believe that this is not a duplicate.

Reproduction link

Steps to reproduce

Drag a file precicely on the border of the child component. (It doesn't matter if a border is set or not, but it makes the example easier to reproduce)

What is expected?

I expect that I can drop my file anywhere on the Upload.Dragger compenent, even with children, without the possibility of invoking the native browser behavior.

What is actually happening?

When you exactly drag on the border of a child component in the dragger area, the dragger area starts to flash. When you then drop at the wrong time, the native browser behavior is invoked (which is opening the file dropped on the viewport)

Environment	Info
antd	3.15.2
React	16.6.3
System	Windows 10
Browser	Chrome 73.0.3683.86

---

A gif of what happens: https://i.imgur.com/CUgsFqT.gifv