fix(http): return after reject so promise doesn't double-settle (#11)

[SAY-5]

Fixes #11. src/http.js had two paths where reject(...) was called but execution continued to a later resolve(result), settling the same promise twice — first as rejected, then as fulfilled (the second settlement is a silent no-op but the wrong outcome wins for the caller's mental model and any logging that observes both signals).

Locations

1. Non-2xx status code (line 22): reject was called, then the request kept draining data/end and the parser eventually invoked resolve(result).
2. XML parse error inside xml2jsparser callback (line 33): reject then resolve(result) ran on the next line unconditionally.

Added return to both reject paths so the function exits cleanly on error.

Test plan

• node -c src/http.js syntax check
• No callers depended on the post-reject continuation; the resolve was unreachable in practice for most consumers but the spurious follow-on resolve(undefined) from the parser path could produce confusing logs