在shape为smooth下，雷达图的line和area之间有缝隙

- [x] I have searched the [issues](https://github.com/antvis/f2/issues) of this repository and believe that this is not a duplicate.

### Reproduction link
[](https://codesandbox.io/s/icy-sunset-fkokx?file=/src/index.js)

### Steps to reproduce
打开就能看到

### What is expected?
期望area和line之间没有空隙

### What is actually happening?
area和line之间有空隙

| Environment | Info |
|---|---|
| f2 | 3.4.3 |
| System | macos |
| Browser | chrome 81.0.4044.138（正式版本） （64 位） |

Start with the linked CodeSandbox reproduction and inspect src/index.js for the smooth radar chart setup. Trace the line and area rendering involved in that example, then verify the chart renders without a gap between them in the reproduction.

Written by the indexing model from the issue text.