Bugfix: Show token string if link name is empty in FileLinkSidebar

owncloud-js-client was parsing empty link name xml attribute as empty object. The empty object was changed with
an empty string. Also, FileLinkSidebar behaviour fixed by showing token as name for the link shares without a name.

https://github.com/owncloud/web/pull/3297
https://github.com/owncloud/web/issues/2517
