geoSort should create GeoDistanceSortDefinition with empty geohashes

[saucam]

When geoSort is used with GeoPoint parameters:

geoSort("location") points List(new GeoPoint(lat, lon)) unit KILOMETERS geoDistance sortMode order SortOrder.DESC

it throws:

Geo distance sorting needs at least one point.
java.lang.IllegalArgumentException: Geo distance sorting needs at least one point.
	at org.elasticsearch.search.sort.GeoDistanceSortBuilder.<init>(GeoDistanceSortBuilder.java:130)
	at org.elasticsearch.search.sort.SortBuilders.geoDistanceSort(SortBuilders.java:88)
	at com.sksamuel.elastic4s.searches.sort.GeoDistanceSortDefinition.<init>(GeoDistanceSortDefinition.scala:13)
	at com.sksamuel.elastic4s.searches.sort.SortDsl$GeoSortExpectsPoints.points(SortDsl.scala:27)

This is because internally this goes to :

def points(points: Iterable[GeoPoint]): GeoDistanceSortDefinition =
      new GeoDistanceSortDefinition(field, Nil, points.toSeq)

which calls

val builder = SortBuilders.geoDistanceSort(field, geohashes: _*).points(points: _*)

inside GeoDistanceSortDefinition
This calls a constructor that always expects a geohash in GeoDistanceSortBuilder,
instead of using the other constructor that expects GeoPoints

 public GeoDistanceSortBuilder(String fieldName, String ... geohashes) {
        if (geohashes.length == 0) {
            throw new IllegalArgumentException("Geo distance sorting needs at least one point.");
        }
...

[saucam]

#704