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FormatMessage only writes the output pointer when it succeeds. On failure it returns 0 and leaves lpMsgBuf untouched, so constructing a std::string from it ran strlen over an indeterminate stack value. Initialize the pointer, check FormatMessage's return, and fall back to reporting the raw system error code. Also release the buffer that FORMAT_MESSAGE_ALLOCATE_BUFFER allocates, which previously leaked on every successful call. Fixes #3714 Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_012SRueobKykUocB1SRdHsEE
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FormatMessage leaves the output pointer untouched when it fails, and getErrorMessage read it uninitialized and never freed the buffer on success. Check the result, return a fallback with the system error code, and LocalFree the buffer. Fixes #3714.