TriangleMesh::doLoad() asserts 'fileName' contains a valid mesh.
In MeshShape::doLoad(), asserts the success of m_initialMesh->doLoad().

Add UnitTest
OctreeShape::doLoad() asserts the success of m_rootNode->doLoad()

Also, after load, OctreeShape::doLoad() will assert the loaded Octree is
valid. Otherwise, assertion will fail.

Add UnitTests for nonexistent and invalid files.