Description:
------------
If you configure a SoapClient with both `exceptions` and `trace` set to TRUE, and the server errors with a SoapFault, the client throws a php SoapFault exception.

In php 5.6, if the SoapFault was caught, you could ask the SoapClient for the request `SoapClient::__getLastRequest()` and response `SoapClient::__getLastResponse()` to investigate the issue. However with php 7.1, and 7.0 it seems, both methods return an empty string if a SoapFault was thrown.

Expected behaviour is the return of the failed request and response so you can investigate the issue.

We have been able to reproduce the issues by testing against a mock server created with SoapUI (https://www.soapui.org/downloads/soapui.html) against a simple example wsdl (https://www.tutorialspoint.com/wsdl/wsdl_example.htm), by setting the response to always be a SoapFault.

Test script:
---------------
<?php
$soapClient = new SoapClient(
    './HelloService.wsdl',
    [
        'location' => 'http://127.0.0.1:8080',
        'trace' => true,
        'exceptions' => true
    ]
);

try {
    $soapClient->sayHello('Php');
} catch (SoapFault $exception) {
    echo 'Request: ' . trim($soapClient->__getLastRequest()) . PHP_EOL;
    echo PHP_EOL;
    echo 'Response: ' . trim($soapClient->__getLastResponse()) . PHP_EOL;
}

Expected result:
----------------
Request: <XML REQUEST>

Response: <XML RESPONSE>

Actual result:
--------------
Request: 

Response: