MINOR: checks: Don't try to send outgoing data if waiting to be able to send

It is useless to try to send outgoing data if the check is still waiting to be
able to send data.

No backport needed.

(cherry picked from commit d94653700437430864c03090d710b95f4e860321)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/checks.c b/src/checks.c
index 90ccff1..901deb9 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -2654,6 +2654,10 @@
 	 *    TCPCHK_ACT_SEND. */
 	else if (check->current_step && check->current_step->action == TCPCHK_ACT_SEND) {
 		if (conn && b_data(&check->bo)) {
+			/* We're already waiting to be able to send, give up */
+			if (check->wait_list.events & SUB_RETRY_SEND)
+				goto out;
+
 			ret = conn->mux->snd_buf(cs, &check->bo,
 						 (IS_HTX_CONN(conn) ? (htxbuf(&check->bo))->data: b_data(&check->bo)), 0);
 			if (ret <= 0) {