http: fix undefined error in parser event

The current check for socket.server[kIncomingMessage] does not
account for the possibility of a socket.server that doesn't
have that property defined. Fix it.

Backport-PR-URL: https://github.com/nodejs/node/pull/22880
PR-URL: https://github.com/nodejs/node/pull/20029
Fixes: https://github.com/nodejs/node/issues/19231


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Khaidi Chu <i@2333.moe>