fix: handle plugin entry file loading when cache temp directory is cleared

[guqing]

What type of PR is this?

/kind bug
/area plugin
/milestone 2.17.x

What this PR does / why we need it:

修复当插件入口文件的缓存目录被系统清理后会导致一直无法加载的问题

原问题复现步骤：

1. 登录后刷新页面，此时缓存目录被创建
2. 删除缓存目录后就会提示文件不存在然后导致插件入口文件一致无法加载直到重启 Halo

Which issue(s) this PR fixes:

Fixes #6226

Does this PR introduce a user-facing change?

修复当插件入口文件的缓存目录被系统清理后会导致一直无法加载的问题

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 57.17%. Comparing base (bc10336) to head (efaee42).
Report is 48 commits behind head on main.

Files	Patch %	Lines
...core/extension/service/impl/PluginServiceImpl.java	72.72%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6238      +/-   ##
============================================
+ Coverage     54.51%   57.17%   +2.66%     
- Complexity     3523     3720     +197     
============================================
  Files           646      648       +2     
  Lines         21862    21988     +126     
  Branches       1528     1542      +14     
============================================
+ Hits          11917    12572     +655     
+ Misses         9328     8805     -523     
+ Partials        617      611       -6     

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[ruibaby]

/lgtm

[JohnNiang]

/lgtm

[f2c-ci-robot]

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This pull-request has been approved by: JohnNiang

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