Update FacebookOAuth2Service.php

[vbuchyn]

Service::checkError() returns error.
protected function checkError()
{
if (isset($_GET[$this->errorParam])) {
$error_code = $_GET[$this->errorParam];
// HERE $this->errorParam == '200', must be 'access_denied' ;
if ($error_code === $this->errorAccessDeniedCode) {
// access_denied error (user canceled)
$this->cancel();
} else {
$error = $error_code;
if (isset($_GET[$this->errorDescriptionParam])) {
$error = $_GET[$this->errorDescriptionParam] . ' (' . $error . ')';
}
throw new ErrorException($error);
}
return false;
}

    return true;
}