fix: default theme invalid time error

[avennn]

🤔 这个变动的性质是？/ What is the nature of this change?

• [ ] 新特性提交 / New feature
• [x] bug 修复 / Fix bug
• [ ] 样式优化 / Style optimization
• [ ] 代码风格优化 / Code style optimization
• [ ] 性能优化 / Performance optimization
• [ ] 构建优化 / Build optimization
• [ ] 网站、文档、Demo 改进 / Website, documentation, demo improvements
• [ ] 重构代码或样式 / Refactor code or style
• [ ] 测试相关 / Test related
• [ ] 其他 / Other

🔗 相关 Issue / Related Issue

暂无相关issue，复现demo，操作步骤demo的README.md有描述

💡 需求背景和解决方案 / Background or solution

问题：使用dumi开发文档系统时，因为组件有使用到date-time-format-timezone，在组件文档路由切换过程中报错。

原因：date-time-format-timezone polyfill了Date对象的toLocaleDateString，最终使用Intl.DateTimeFormat来格式化时间。而默认主题的layout.tsx文件中，const updatedTimeIns = new Date(meta.updatedTime)在组件切换过程meta.updatedTime有可能为undefined，对应updatedTimeIns为Invalid Date对象，调用toLocaleDateString（实际Intl.DateTimeFormat）就会报错：

修复方式： 当meta.updatedTime为undefined时，生成的updatedTime为”Invalid Date Invalid Date"，展示在页面上没有意义 所以，只有当meta.updatedTime有值时才执行原来的格式化的逻辑。

📝 更新日志 / Changelog

Language	Changelog
🇺🇸 English	fix invalid date error when switch between component routes
🇨🇳 Chinese	修复切换组件路由时invalid date的错误

[vercel[bot]]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated
dumi	❌ Failed (Inspect)		Jun 24, 2022 at 3:58PM (UTC)

[github-actions[bot]]

🎊 PR Preview has been successfully built and deployed to https://dumi-preview-pr-1116.surge.sh

[github-actions[bot]]

🎊 PR Mobile Preview has been successfully built and deployed to https://dumi-mobile-preview-pr-1116.surge.sh

[codecov[bot]]

Codecov Report

Merging #1116 (f859b67) into master (202b2c8) will decrease coverage by 0.12%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1116      +/-   ##
==========================================
- Coverage   95.06%   94.93%   -0.13%     
==========================================
  Files         119      119              
  Lines        2937     2942       +5     
  Branches      972     1003      +31     
==========================================
+ Hits         2792     2793       +1     
- Misses        141      145       +4     
  Partials        4        4              

Impacted Files	Coverage Δ
packages/theme-default/src/layout.tsx	94.54% <100.00%> (+0.10%)	:arrow_up:
packages/theme-default/src/builtins/Previewer.tsx	87.83% <0.00%> (-5.02%)	:arrow_down:

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[PeachScript]

❤️ 感谢贡献，dumi v1 不再更新，PR 将会关闭；dumi v2 已发布，欢迎继续参与 dumi 的建设，https://d.umijs.org/