test_ogrsf: avoid exit(1) in a now-threaded function

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@26327 f0d54148-0727-0410-94bb-9a71ac55c965
Fix inverted logic in OGRGeometry::UnionCascaded() (fix r26326)

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@26328 f0d54148-0727-0410-94bb-9a71ac55c965