SoapServer handle() method doesn't work without the $soap_request argument

The docs for `public function handle ([ string $soap_request ] ): void` say that _"If this argument is omitted, the request is assumed to be in the raw POST data of the HTTP request"_. This doesn't seem to work like this under HHVM. If you omit giving the $soap_request parameter you'll get a "Bad request" response.

``` php
$server = new SoapServer(null, array(
'uri'=> 'http://www.example.com/',
'encoding'=>'UTF-8',
'soap_version' => SOAP_1_2,
));

$server->setClass('MyClass');

/* Not working */
$server->handle();

/* Working */
$server->handle(file_get_contents("php://input"));
```

See also [this Stackoverflow entry](http://stackoverflow.com/questions/28363769/soapserver-on-hhvm-throws-a-bad-request-soapfault)