BUG/MEDIUM: checks: Be sure to subscribe for sends if outgoing data remains

When some data are scheduled to be sent, we must be sure to subscribe for sends
if nothing was sent. Because of a bug, when nothing was sent, connection errors
are checks. If no error is found, we exit, waiting for more data, without any
subcription on send events.

No need to backport.
diff --git a/src/checks.c b/src/checks.c
index 6f707fb..0ea389e 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -1983,10 +1983,10 @@
 	};
 
 	if (conn->mux->snd_buf(cs, &check->bo, b_data(&check->bo), 0) <= 0) {
-		ret = TCPCHK_EVAL_WAIT;
-		if ((conn->flags & CO_FL_ERROR) || (cs->flags & CS_FL_ERROR))
+		if ((conn->flags & CO_FL_ERROR) || (cs->flags & CS_FL_ERROR)) {
 			ret = TCPCHK_EVAL_STOP;
-		goto out;
+			goto out;
+		}
 	}
 	if (b_data(&check->bo)) {
 		cs->conn->mux->subscribe(cs, SUB_RETRY_SEND, &check->wait_list);
@@ -2388,7 +2388,6 @@
 			if (ret <= 0) {
 				if ((conn && conn->flags & CO_FL_ERROR) || (cs && cs->flags & CS_FL_ERROR))
 					goto out_end_tcpcheck;
-				goto out;
 			}
 			if (b_data(&check->bo)) {
 				cs->conn->mux->subscribe(cs, SUB_RETRY_SEND, &check->wait_list);