http: fix parsing of binary upgrade response body
Fix a bug where a connection upgrade response with a Transfer-Encoding header and a body whose first byte is > 127 causes said byte to be dropped on the floor when passing the remainder of the message to the 'upgrade' event listeners.
Fixes: https://github.com/nodejs/node/issues/17789 CI: https://ci.nodejs.org/job/node-test-commit/15003/