Fail on select() failing in stratum thread without needing to attempt recv_line.

cgminer.c

@@ -4333,7 +4333,9 @@ static void *stratum_thread(void *userdata)
 		 * every minute so if we fail to receive any for 90 seconds we
 		 * assume the connection has been dropped and treat this pool
 		 * as dead */
-		select(pool->sock + 1, &rd, NULL, NULL, &timeout);
+		if (unlikely(select(pool->sock + 1, &rd, NULL, NULL, &timeout) < 1))
+			s = NULL;
+		else
 			s = recv_line(pool);
 		if (!s) {
 			applog(LOG_INFO, "Stratum connection to pool %d interrupted", pool->pool_no);