MEDIUM: stream-int: fix the si_cant_put() calls used for buffer readiness

A number of calls to si_cant_put() were used in fact to request being
called back once a buffer is available. These ones are not needed anymore
since si_alloc_ibuf() already sets the SI_FL_RXBLK_BUFF flag when called
in appctx context. Those called with a foreign stream-int are simply turned
to si_rx_buff_blk().

src/cli.c

@@ -550,7 +550,9 @@ static void cli_io_handler(struct appctx *appctx)
 
 	/* Check if the input buffer is avalaible. */
 	if (res->buf.size == 0) {
-		si_cant_put(si);
+		/* buf.size==0 means we failed to get a buffer and were
+		 * already subscribed to a wait list to get a buffer.
+		 */
 		goto out;
 	}