http: call write callback even if there is no message body

Ensure that the callback of `OutgoingMessage.prototype.write()` is
called when `outgoingMessage._hasBody` is `false` (HEAD method, 204
status code, etc.).

Refs: https://github.com/nodejs/node/pull/27709

PR-URL: https://github.com/nodejs/node/pull/27777


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>