Path based requests are flaky

When having fun with https://github.com/owncloud/ocis/pull/7250 I noticed that path based requests are flaky. Path based ListContainer requests for `/users/some-u-u-i-d` sometimes are routed to the sharesstorageprovider because that is mounted at `/users/some-u-u-i-d/Shares`. The gateway just picks the first storage provider it encounters which then returns a not found error.