HTTP/2 PUSH_PROMISE DoS

Summary: In `discard_newhandle` the condition in the `if` statement is always `false` for http transfer due to a negation. As a result `http2_data_done` will never be called.

static void discard_newhandle(struct Curl_cfilter *cf,
                              struct Curl_easy *newhandle)
{
  if(!newhandle->req.p.http) {
    http2_data_done(cf, newhandle, TRUE);
    newhandle->req.p.http = NULL;
  }
  (void)Curl_close(&newhandle);
}