Indexed objects loose association with attributes when indexed as array

ES creates the array at _content, not the object and therefore attributes can no longer be associated with their actual element.

Steps to reproduce:

Index any element with attributes as array.

Example: Find http://nbn-resolving.de/urn:nbn:de:bvb:12-bsb00029380-5

(from redmine: issue id 39, created on 2018-01-22tgradl, closed on 2018-01-22)