fix getProfile logic

[TavoNiievez]

Calling:

$this->client->getResponse();

results in:

[BadMethodCallException] The "request()" method must be called before "AbstractBrowser::getRe
sponse()".

so this is never reached:

if (null === $response) {
    $this->fail("You must perform a request before using this method.");
}
return $profiler->loadProfileFromResponse($response);