柱状图开启滚动条（scrollbar），如果轴标签显示数量（tickCount）太少的话，会造成标签没有均匀分布，只显示前边部分，后边部分不显示🐛 [BUG]

### 🐛 Bug description [Please make everyone to understand it]
柱状图开启滚动条（scrollbar），如果轴标签显示数量（tickCount）太少的话，会造成标签没有均匀分布，只显示前边部分，后边部分不显示🐛

> Please provide a link by forking these links [G2Plot](https://codesandbox.io/s/g2plot-issue-template-gzfdq?file=/index.ts) or GitHub repo, a minimal reproduction.

* _Required_ **Link to minimal reproduction**:

### 📷 Step to reproduce

复现链接：https://codesandbox.io/s/great-browser-xhrgs0?file=/index.ts

### 🏞 Expected result

### 🚑 Any additional [like screenshots]

* **G2Plot Version**:2.4.20
* **Platform**:

Start with the linked CodeSandbox reproduction and G2Plot version 2.4.20, using a bar chart with scrollbar enabled and a small tickCount. Trace how axis labels are laid out when scrolling, then verify that labels remain distributed across the full data range rather than appearing only at the beginning.

Written by the indexing model from the issue text.