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Fix RequestHeader.ContentLength() if disableSpecialHeader is true ( 2042)

Fix RequestHeader.ContentLength() if disableSpecialHeader is true ( 2042): a task in repo2rlenv-commit-runtime-v2 (Harbor dataset). Title: RequestHeader.ContentLength() returns wrong value when special headers are disabled

The task

**Title:** `RequestHeader.ContentLength()` returns wrong value when special headers are disabled

Part of FineEnvs/repo2rlenv-commit-runtime.