fix: regression for custom configurations

[alexander-akait]

What kind of change does this PR introduce?

fixes #3833

Did you add tests for your changes?

yes

If relevant, did you update the documentation?

No need

Summary

Fix regression

Does this PR introduce a breaking change?

No

Other information

No

[codecov]

Codecov Report

Merging #3834 (ac7c27d) into master (14b9c18) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3834   +/-   ##
=======================================
  Coverage   91.39%   91.39%           
=======================================
  Files          22       22           
  Lines        1673     1673           
  Branches      484      484           
=======================================
  Hits         1529     1529           
  Misses        144      144           

Impacted Files	Coverage Δ
packages/webpack-cli/src/webpack-cli.ts	92.60% <100.00%> (ø)

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