BUG/MINOR: stats/htx: Remove channel's output when the request is eaten

The request is eaten when the stats applet have finished to send its
response. It was removed from the channel's buffer, removing all HTX blocks till
the EOM. But the channel's output was not reset, leaving the request channel in
an undefined state.

src/stats.c

@@ -3246,6 +3246,7 @@ static void htx_stats_io_handler(struct appctx *appctx)
 			if (type == HTX_BLK_EOM)
 				break;
 		}
+		co_set_data(req, 0);
 		if (htx_is_empty(req_htx)) {
 			htx_reset(req_htx);
 			b_set_data(&req->buf, 0);