Bug #361: Bad DNs in ACIs can segfault ns-slapd

A bad userdn will make the DN normalization fail.  This sets dn to NULL,
and the server will attempt to access the NULL dn.
The fix is to just return with an error if the normalization fails since
the DN is invalid.
Reviewed by: rmeggins

ldap/servers/plugins/acl/aclparse.c

@@ -566,6 +566,11 @@ __aclp__copy_normalized_str (char *src, char *endsrc, char *start,
 		/* Normalize the value of userdn and append it to ret_str */
 		slapi_sdn_init_dn_byref(&sdn, p);
 		dn = slapi_sdn_get_dn(&sdn);
+		/* Normalization failed so return an error (-1) */
+		if (!dn) {
+			slapi_sdn_done(&sdn);
+			return -1;
+		}
 		/* append up to ldap(s):/// */
 		aclutil_str_append_ext(dest, destlen, start, p - start);
 		/* append the DN part */