fix for mesh-based views


git-svn-id: https://geuz.org/svn/gmsh/trunk@17391 59c8cabf-10d6-4a28-b43f-3936b85956c4
fixes from Robin Huart


git-svn-id: https://geuz.org/svn/gmsh/trunk@17392 59c8cabf-10d6-4a28-b43f-3936b85956c4