socks: ensure DNS is freed in failure cases.

[cmeister2]

In several error cases in socks.c the DNS struct is not freed, which leads to memory leaks.

Found by: OSS-Fuzz: 447858136

Closes #20813

[testclutch]

Analysis of PR #20813 at a05120f4:

Test ../../tests/http/test_05_errors.py::TestErrors::test_05_01_partial_1[h3] failed, but it has been 0.8% flaky lately, so it's probably NOT a fault of the PR. Note that this test has failed in 2 different CI jobs (the link just goes to one of them).

Generated by Testclutch

[bagder]

@aisle-analyzer augment review

[aisle-research-bot]

🔒 Aisle Security Analysis

✅ We scanned this PR and did not find any security vulnerabilities.

_{Aisle supplements but does not replace security review.}

---

Analyzed PR: #20813 at commit a05120f

_{Last updated on: 2026-03-04T16:43:02Z}

[augmentcode]

🤖 Augment PR Summary

Summary: Ensures SOCKS4 hostname resolution cleans up any obtained DNS cache entry in error/unsupported-address paths.
Why: Prevents resolver-related memory leaks in lib/socks.c reported by OSS-Fuzz.

_{🤖 Was this summary useful? React with 👍 or 👎}

[augmentcode]

Review completed. No suggestions at this time.

Comment augment review to trigger a new review at any time.