Fix pg_ctl initdb without options.

Passing NULL string to snprintf is avoided.

src/bin/pg_ctl/pg_ctl.c

@@ -4,7 +4,7 @@
  *
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/bin/pg_ctl/pg_ctl.c,v 1.116 2009/12/10 06:32:28 petere Exp $
+ * $PostgreSQL: pgsql/src/bin/pg_ctl/pg_ctl.c,v 1.117 2009/12/15 00:17:50 itagaki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -656,6 +656,9 @@ do_init(void)
 	if (exec_path == NULL)
 		exec_path = find_other_exec_or_die(argv0, "initdb", "initdb (PostgreSQL) " PG_VERSION "\n");
 
+	if (pgdata_opt == NULL)
+		pgdata_opt = "";
+
 	if (post_opts == NULL)
 		post_opts = "";