ylpodview - fix to enable StackTrace.

* Use of Plack::App::Cascade was the cause of scope guard bypassing problem.

If I wrap $app with Plack::App::Cascade, inner most $app will be called
outside of all middlewares. This is because ``Plack::App::Cascade->call``
just returns ``sub {}``. Actuall processing is handled through
last ``if (ref $res eq 'CODE')...`` part of handle_connection.