BUG/MINOR: mux-h1: do not skip the error response on bad requests

Since 2.4-dev3 with commit c4bfa59f1 ("MAJOR: mux-h1: Create the client
stream as later as possible"), a request error doesn't result in any
error response if "option http-ignore-probes" is set, there's just a
close. This is caused by an unneeded b_reset() in h1_process_demux()'s
error path, which makes h1_handle_bad_req() believe there was an empty
request. There is no reason for this reset to be there, it must have
been a leftover of an earlier attempt at dealing with the error, let's
drop it.

This should be backported to 2.4.

src/mux_h1.c

@@ -1711,7 +1711,6 @@ static size_t h1_process_demux(struct h1c *h1c, struct buffer *buf, size_t count
 	return ret;
 
   err:
-	b_reset(&h1c->ibuf);
 	htx_to_buf(htx, buf);
 	if (h1s->cs)
 		h1s->cs->flags |= CS_FL_EOI;