Fix bug #9360-revival: fix whole layer not rendered (when simplify geometry activated)

Ths patch fixes the bug #9360 when the code was translated from OGRGeometry* to OGRGeometryH classes in commit (https://github.com/qgis/QGIS/commit/3305a6c77903f1ef9cce012f52ff49c8e35f269a)

Changes:
+ Restore OGRGeometry* management to redim the simplified geometry with 'lineString->setPoints( numPoints, points )'
+ Restore the shared point buffer managed to optimize the memory in simplification of large datasets