fix crash on delete (Sphere_1.brep)


git-svn-id: https://geuz.org/svn/gmsh/trunk@16752 59c8cabf-10d6-4a28-b43f-3936b85956c4
QuadTri documentation + clarify animations


git-svn-id: https://geuz.org/svn/gmsh/trunk@16753 59c8cabf-10d6-4a28-b43f-3936b85956c4