Add cunit test for #2307

So now we have a "leak or crash" situation.

git-svn-id: http://svn.osgeo.org/postgis/trunk@11635 b70326c6-7e19-0410-871a-916f4a2858ee
Fix the ST_MakeValid leak, keep it crash-free (#2307)

git-svn-id: http://svn.osgeo.org/postgis/trunk@11636 b70326c6-7e19-0410-871a-916f4a2858ee