add skipif (needs json)

Author: remicollet

ext/standard/tests/url/base64_decode_basic_003.phpt

@@ -1,5 +1,7 @@
 --TEST--
 Test base64_decode() function : basic functionality - padding and whitespace
+--SKIPIF--
+<?php if (!extension_loaded("json")) print "skip"; ?>
 --FILE--
 <?php
 /* Prototype  : proto string base64_decode(string str[, bool strict])