stroke: stop enumerating IKE_SAs in statusall if output stream gets closed

If the output stream is not interested in more information, it can close the
the stream. Checking for stream errors avoids useless enumeration of IKE_SAs,
saving resources. This allows to use "ipsec statusall | head" to monitor the
daemon, or stop enumerating IKE_SAs after a specific entry has been found.

src/libcharon/plugins/stroke/stroke_list.c

@@ -647,7 +647,7 @@ METHOD(stroke_list_t, status, void,
 		half_open);
 	enumerator = charon->controller->create_ike_sa_enumerator(
 													charon->controller, wait);
-	while (enumerator->enumerate(enumerator, &ike_sa))
+	while (enumerator->enumerate(enumerator, &ike_sa) && ferror(out) == 0)
 	{
 		bool ike_printed = FALSE;
 		enumerator_t *children = ike_sa->create_child_sa_enumerator(ike_sa);