[PATCH] Allow null to string conversion for PHP 6

Playing around with PHP 6 I noticed that some functions start to
complain about conversion of null values to strings:

php -d error_reporting=65535 -r 'var_dump(urldecode(null));'

Warning: urldecode() expects parameter 1 to be strictly a binary string,
null given in Command line code on line 1

I think this is wrong and attached a patch against HEAD to fix this.
Note: While the patch seems a bit hacky at first it is IMHO the simplest
solution without having to resort to copy/paste or goto. But if you want
another solution I'm happy with that too :-)

• Chris