[8.x] fix Request offsetExists without routeResolver

[danesteve]

When checking if a request parameter isset without the routeResolver being set we get an error.

Example:

isset((new \Illuminate\Http\Request())['foobar']);
// or
(new \Illuminate\Http\Request())['foobar'] ?? '';

// throws the following error
// PHP Error:  Call to a member function parameters() on null