garden test crash on ST_ClusterKMeans

[robe]

Testing PostGIS 2.5.0alpha on postgreSQL 10.1 windows and 11beta1

SELECT ST_ClusterKMeans(foo1.the_geom, 3)OVER()  As result
  FROM ((SELECT ST_Collect(geom)  As the_geom
		FROM (VALUES ( ST_GeomFromEWKT('SRID=4326;MULTIPOLYGON(((-71.0821 42.3036 2,-71.0822 42.3036 2,-71.082 42.3038 2,-71.0819 42.3037 2,-71.0821 42.3036 2)))') ),
	( ST_GeomFromEWKT('SRID=4326;POLYGON((-71.1261 42.2703 1,-71.1257 42.2703 1,-71.1257 42.2701 1,-71.126 42.2701 1,-71.1261 42.2702 1,-71.1261 42.2703 1))') ) ) As g(geom) CROSS JOIN generate_series(1,3) As i GROUP BY i )) As foo1 LIMIT 10; 

[komzpa]

reproduces on POSTGIS="2.5.0dev r16548" [EXTENSION] PGSQL="100" GEOS="3.7.0dev-CAPI-1.11.0 0" SFCGAL="1.3.1" PROJ="Rel. 4.9.3, 15 August 2016" GDAL="GDAL 2.3.0, released 2018/05/04" LIBXML="2.9.4" LIBJSON="0.12.1" LIBPROTOBUF="1.3.0" RASTER

looking into it.

[komzpa]

minimized version:

 select ST_ClusterKMeans(geom,2) over() from (values ('POINT(0 0)'::geometry), ('POINT(0 0)')) g(geom);

[komzpa]

In 16604:

Let KMeans init even if there are only duplicates in input

Added reporting of duplicates noticed on init pass.

Closes #4100
Closes ​https://github.com/postgis/postgis/pull/253