Bugfix: load folder in Media viewer

We've fixed the loading of a folder in the Media viewer extension.
If a user reloads the Media viewer now, it load all the medias both in private and public context.

https://github.com/owncloud/web/issues/5427
https://github.com/owncloud/web/pull/5585
https://github.com/owncloud/web/pull/5710
