Fixed race condition which results in inconsistent error code on missing copyright header.

[vovanec]

Fixed race condition which resulted in inconsistent error code on missing copyright header.

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[vovanec]

@googlebot I signed it!

[vovanec]

Is there ANY ongoing activity for this project? I see a bunch of merge requests opened without any update. If it's not something actively maintained by anybody, I can take over or simply do my own fork. Let me know.