http: check for existance in resetHeadersTimeoutOnReqEnd

socket.parser can be undefined under unknown circumstances.
This is a fix for a bug I cannot reproduce but it is affecting
people.

Fixes: https://github.com/nodejs/node/issues/26366

PR-URL: https://github.com/nodejs/node/pull/26402


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>