fix(plugin): prevent require.resolve paths arguments undefined

[noahziheng]

related #229

1.0.4 版本可能造成使用预先生成的 manifest 文件时，因为缺少扫描器补入的 baseDir（对 package 字段意义不大）造成 require.resolve 失败

代码很早之前就在，之前未触发的主要原因是：

• Scanner 之前基于避免非必要合并的考虑，剔除了 plugin-config loader 的全部 item，所以确实 loaderState.baseDir 的 item 不会进入运行时的 loader
• 重构期间为了对齐所有 config 的合并逻辑，移除了剔除 item 的代码

[codecov-commenter]

Codecov Report

Base: 92.76% // Head: 92.76% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (67742ad) compared to base (c86b7b5).
Patch coverage: 100.00% of modified lines in pull request are covered.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #231   +/-   ##
=======================================
  Coverage   92.76%   92.76%           
=======================================
  Files          54       54           
  Lines        1299     1300    +1     
  Branches      225      225           
=======================================
+ Hits         1205     1206    +1     
  Misses         94       94           

Impacted Files	Coverage Δ
src/plugin/factory.ts	100.00% <100.00%> (ø)

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