Fix work packages menu item never being selected

https://www.openproject.org/work_packages/15441

For query menu items this already worked, but the work packages main
item was never selected.
To be honest, I'm not sure why it's sometimes `null` and sometimes `undefined`.

Rather than having to mess around with explicit coercion, I guess I'd probably use the double equals operator here: `scope.queryId == $stateParams.query_id`