MINOR: h2: pre-initialize h1m->err_pos to -1 on the output path

We don't want to trigger an error while parsing a response coming from
haproxy (it could be an errorfile for example), so let's set this to
-1.

src/mux_h2.c

@@ -691,6 +691,7 @@ static struct h2s *h2c_stream_new(struct h2c *h2c, int id)
 	h2s->st        = H2_SS_IDLE;
 	h2s->rxbuf     = BUF_NULL;
 	h1m_init_res(&h2s->h1m);
+	h2s->h1m.err_pos = -1; // don't care about errors on the response path
 	h2s->by_id.key = h2s->id = id;
 	h2c->max_id    = id;
 
@@ -3231,6 +3232,7 @@ static size_t h2s_frt_make_resp_headers(struct h2s *h2s, const struct buffer *bu
 	else if (h1m->status >= 100 && h1m->status < 200) {
 		/* we'll let the caller check if it has more headers to send */
 		h1m_init_res(h1m);
+		h1m->err_pos = -1; // don't care about errors on the response path
 		goto end;
 	}
 	else