…URL without request

Currently the LogoutUrlGenerator will raise an Error if called without a current request present because it does not check if there is a request present before using it.
The error that is raised is: Call to a member function getBaseUrl() on null on line 110 (line 114 with this patch applied)

In my use-case, this get's called by Symfony\Bundle\SecurityBundle\DataCollector\SecurityDataCollector::collect() using the following code:

$logoutUrl = null;
try {
    if (null !== $this->logoutUrlGenerator && !$token instanceof AnonymousToken) {
        $logoutUrl = $this->logoutUrlGenerator->getLogoutPath();
    }
} catch (\Exception $e) {
    // fail silently when the logout URL cannot be generated
}

The above code inside the SecurityDataCollector tries to "fail silently" if no logout-URL cannot be generated. But this silent-fail fails itself because the thrown "exception" is not an \Exception, but an \Error instead (\Error is not an descendant of \Exception, so it does not get catched here).

In order to resolve this situation, the proposed patch makes the LogoutUrlGenerator explicitly test if a request is actually present and then throw a \LogicException instead of an \Error if that check fails.