Fix bug where pg_receivexlog goes into busy loop if -s option is set to 0.

The problem is that pg_receivexlog calls select(2) with timeout=0 and
goes into busy loop when --status-interval option is set to 0. This bug
was introduced by the commit,
74cbe966fe2d76de1d607d933c98c144dab58769.

Per report from Sawada Masahiko

src/bin/pg_basebackup/receivelog.c

@@ -1094,7 +1094,7 @@ CopyStreamReceive(PGconn *conn, long timeout, char **buffer)
 		 * No data available. Wait for some to appear, but not longer than
 		 * the specified timeout, so that we can ping the server.
 		 */
-		if (timeout > 0)
+		if (timeout != 0)
 		{
 			int		ret;