Bug 630091 - (cov#15582) Free of uninitialized pointer in attr_index_config()

In attr_index_config(), if argc or argv are NULL, we jump to the
done label.  We then try to free attrs, but it was never initialized.
We need to initialize attrs to NULL.

ldap/servers/slapd/back-ldbm/ldbm_attr.c

@@ -178,7 +178,7 @@ attr_index_config(
 {
 	ldbm_instance *inst = (ldbm_instance *) be->be_instance_info;
 	int	i, j;
-	char	**attrs;
+	char	**attrs = NULL;
 	char	**indexes = NULL;
 	char	**index_rules = NULL;
 	struct attrinfo	*a;