Bug 18189 - Elasticsearch sorting broken

Bug 18189 - Elasticsearch sorting broken

To test:
1 - Have ES enabled and biblios and authorities indexed
2 - Perform a catalog search
3 - Try to sort results by author, it will fail
4 - Perform an authority search with sorting enabled, it will fail
5 - Apply patch
6 - Reindex, deleting current indexes
    perl /home/vagrant/kohaclone/misc/search_tools/rebuild_elastic_search.pl
    -d -v
7 - Repeat 3&4, they should succeed

Signed-off-by: Srdjan <srdjan@catalyst.net.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>