http: fix error check in `Execute()`
Refs: https://github.com/nodejs/node/pull/24738 Fixes: https://github.com/nodejs/node/issues/25858
CI: https://ci.nodejs.org/job/node-test-pull-request/20501/
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines