clip PolyPolygon::Insert on .svm load

valgrind + bff

Change-Id: Ib3ed8a6e518c0686f8cbeaf021b9ca3a07005032
(cherry picked from commit fd64d444b730f6cb7216dac8f6e3f94b97d7ab60)
Reviewed-on: https://gerrit.libreoffice.org/11381
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>