after router middleware not keeping states?

Hi!

I'm doing something like this

init stuff
$router->before stuff
$router->match stuff

$router->run(afterRouterMiddleware());

The route handling functions are setting some variables in static or singleton objects and everything runs fine between different objects. But the afterRouterMiddleware() function seems to forget all about these states. If i call the function just after $router->run() it runs fine but not as a callback.

I will write a more concrete example:

```
class AccessController
{
public static function authenticateForAdmin() {
User::getInstance()->setId(1337);
}
}
```
```
// bootstrap
$router->before('GET|POST|PUT|DELETE', '/admin/(?!authenticate)(.*)', 'AccessController@isVerifiedAsAdmin');
$router->mount('/admin', function () use ($router) {
$router->match('GET|POST', '/authenticate', 'AccessController@authenticateForAdmin');
}

$router->run(function() {
User::getInstance()->getId(); // <<=== null
});

User::getInstance()->getId(); // <<=== 1337
```

I think this behaviour is not supposed to happen.

Start at the router->run() callback and compare its execution context with calling the same function after run(), using the bootstrap example as the reproduction. Trace how the mounted route and middleware are invoked, then verify that state set by authenticateForAdmin() remains available in the callback.

Written by the indexing model from the issue text.