fix(datepicker): 修复空字符串页面崩溃问题

[honkinglin]

fix #1451

🤔 这个 PR 的性质是？

• 日常 bug 修复
• 新特性提交
• 文档改进
• 演示代码改进
• 组件样式/交互改进
• CI/CD 改进
• 重构
• 代码风格优化
• 测试用例
• 分支合并
• 其他

🔗 相关 Issue

💡 需求背景和解决方案

📝 更新日志

• fix(DatePicker): 修复空字符串页面崩溃问题

• 本条 PR 不需要纳入 Changelog

☑️ 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

[github-actions]

[codecov-commenter]

Codecov Report

Merging #1453 (ab2358e) into develop (492d477) will increase coverage by 3.78%.
The diff coverage is 90.99%.

@@             Coverage Diff             @@
##           develop    #1453      +/-   ##
===========================================
+ Coverage    57.94%   61.73%   +3.78%     
===========================================
  Files          407      643     +236     
  Lines        15371    15689     +318     
  Branches      2931     2803     -128     
===========================================
+ Hits          8907     9685     +778     
+ Misses        6187     5715     -472     
- Partials       277      289      +12     

Impacted Files	Coverage Δ
src/alert/_example/icon.vue	100.00% <ø> (ø)
src/alert/_usage/index.vue	0.00% <ø> (ø)
src/anchor/_usage/index.vue	0.00% <ø> (ø)
src/avatar/_example/base.vue	100.00% <ø> (ø)
src/avatar/_usage/index.vue	0.00% <ø> (ø)
src/badge/_usage/index.vue	0.00% <ø> (ø)
src/breadcrumb/_example/custom.vue	100.00% <ø> (ø)
src/breadcrumb/_example/dropdown.vue	100.00% <ø> (ø)
src/button/_example/icon.vue	100.00% <ø> (ø)
src/button/_usage/index.vue	0.00% <ø> (ø)
... and 457 more

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