Have XMLTester use POINT EMPTY for a null return from getInteriorPoint

git-svn-id: http://svn.osgeo.org/geos/branches/3.3@3745 5242fede-7e19-0410-aef8-94bd7d2200fb
Fix EMPTY return from zero-area polygon (#613)

git-svn-id: http://svn.osgeo.org/geos/branches/3.3@3746 5242fede-7e19-0410-aef8-94bd7d2200fb