🐛交叉表自定义排序会将空字符串置底

### 🏷 Version

| Package | Version |
| -------------- | ------- |
| @antv/s2 | 1.47.1 |
| @antv/s2-react | |
| @antv/s2-vue | |

### Sheet Type

- [x] PivotSheet
- [ ] TableSheet
- [ ] GridAnalysisSheet
- [ ] StrategySheet
- [ ] EditableSheet

### 🖋 Description

交叉表配置自定义排序后，维值中出现的空字符串会置底，无法参与排序
### ⌨️ Code Snapshots

### 🔗 Reproduce Link
https://codesandbox.io/s/falling-pine-9l2v8k?file=/index.ts

### 🤔 Steps to Reproduce
打开Reproduce Link

### 😊 Expected Behavior
维值中的空字符串可以正常参与排序

### 😅 Current Behavior
维值中的空字符串无法参与排序，且会置底

### 💻 System information

| Environment | Info |
| ------- | ------- |
| System | macOS |
| Browser | Chrome |

Start with index.ts in the linked CodeSandbox reproduction and reproduce the issue using @antv/s2 1.47.1 with a PivotSheet and custom sorting. Confirm the fix by checking that empty-string dimension values participate in the configured order instead of being placed last.

Written by the indexing model from the issue text.