Adapt OCE 3D plugin to OpenCascade 7.6.0
OpenCascade 7.6 changes access to the internal arrays of Poly_Triangulation objects. This was noticed in the 5.1 package on FreeBSD, but the same code exists on the master branch, so let's fix it here.
OpenCascade 7.6 changes access to the internal arrays of Poly_Triangulation objects. This was noticed in the 5.1 package on FreeBSD, but the same code exists on the master branch, so let's fix it here.