feat: fix js error if value not in options

[icaife]

🤔 这个变动的性质是？

• 新特性提交
• [ x ] 日常 bug 修复
• 站点、文档改进
• 演示代码改进
• 组件样式/交互改进
• TypeScript 定义更新
• 包体积优化
• 性能优化
• 功能增强
• 国际化改进
• 重构
• 代码风格优化
• 测试用例
• 分支合并
• 其他改动（是关于什么的改动？）

🔗 相关 Issue

💡 需求背景和解决方案

https://codesandbox.io/s/laughing-fog-b12ijp?file=/src/App.js
当labelInValue=true mode=multiple的时候，value不在options内，删除会导致报错。

Select.tsx 447行：
const option = getMixedOption(val); // option可能为undefined,导致 option.key 抛出错误

📝 更新日志

语言	更新描述
🇺🇸 英文
🇨🇳 中文

☑️ 请求合并前的自查清单

⚠️ 请自检并全部勾选全部选项。⚠️

• 文档已补充或无须补充
• 代码演示已提供或无须提供
• TypeScript 定义已补充或无须补充
• Changelog 已提供或无须提供

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🔍 Inspect: https://vercel.com/react-component/select/Hkf9Dcqz6UpECWJajc1Vq51xDNpJ
✅ Preview: https://select-git-fork-icaife-fix-js-error-when-remove-react-component.vercel.app

[afc163]

别改 example，加个用例。

[codecov]

Codecov Report

Merging #723 (c184d24) into master (4bc806f) will not change coverage.
The diff coverage is 100.00%.

❗ Current head c184d24 differs from pull request most recent head 26a68ff. Consider uploading reports for the commit 26a68ff to get more accurate results

@@           Coverage Diff           @@
##           master     #723   +/-   ##
=======================================
  Coverage   99.50%   99.50%           
=======================================
  Files          25       25           
  Lines        1010     1010           
  Branches      320      320           
=======================================
  Hits         1005     1005           
  Misses          4        4           
  Partials        1        1           

Impacted Files	Coverage Δ
src/Select.tsx	100.00% <100.00%> (ø)

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[icaife]

测试用例已加，还原了example