DrawMesh<Hexahedron> does not check the consistency of the topology

[fredroy]

Problem

When using a SparseGrid and something drawing the associated hexahedra using DrawMesh (for example HexahedronFEMForcefield and rendering the FEM), then it is crashing because it is expecting having the associated quads composing the hexahedra. It seems that SparseGrid does only create the hexahedra.

Steps to reproduce
Simple Scene:

<Node name="root" gravity="0 0 0"  dt="0.04">
    <Node name="plugins" >
        <RequiredPlugin pluginName="Sofa.Component.Constraint.Projective"/> <!-- Needed to use components [FixedProjectiveConstraint] -->
        <RequiredPlugin pluginName="Sofa.Component.Engine.Select"/> <!-- Needed to use components [BoxROI] -->
        <RequiredPlugin pluginName="Sofa.Component.IO.Mesh"/> <!-- Needed to use components [MeshOBJLoader] -->
        <RequiredPlugin pluginName="Sofa.Component.LinearSolver.Iterative"/> <!-- Needed to use components [CGLinearSolver] -->
        <RequiredPlugin pluginName="Sofa.Component.Mapping.Linear"/> <!-- Needed to use components [BarycentricMapping] -->
        <RequiredPlugin pluginName="Sofa.Component.Mass"/> <!-- Needed to use components [UniformMass] -->
        <RequiredPlugin pluginName="Sofa.Component.ODESolver.Backward"/> <!-- Needed to use components [EulerImplicitSolver] -->
        <RequiredPlugin pluginName="Sofa.Component.SolidMechanics.FEM.Elastic"/> <!-- Needed to use components [HexahedronFEMForceField] -->
        <RequiredPlugin pluginName="Sofa.Component.StateContainer"/> <!-- Needed to use components [MechanicalObject] -->
        <RequiredPlugin pluginName="Sofa.Component.Topology.Container.Grid"/> <!-- Needed to use components [SparseGridTopology] -->
        <RequiredPlugin pluginName="Sofa.GL.Component.Rendering3D"/> <!-- Needed to use components [OglModel] -->
    </Node>

    <DefaultAnimationLoop />

    <Node name="DynamicStuff" >
        <EulerImplicitSolver name="cg_odesolver"  />
        <CGLinearSolver name="linear solver" iterations="25" tolerance="1e-15" threshold="1e-15" />

        <Node name="Cylinder" >
            <SparseGridTopology name="grid" n="6 10 6" filename="mesh/cylinder.obj" />
            <MechanicalObject name="mechanicalDofs" />
            <UniformMass  totalMass="1" />
            <HexahedronFEMForceField template="Vec3d" name="FEM" method="large" poissonRatio="0.3" youngModulus="3000" />
            <BoxROI name="bbox" drawBoxes="true" box="-1.05 -0.5 -1.05  1.05 0.5 1.05
                                                      -1.05 9.5 -1.05  1.05 10.5 1.05"  />
            <FixedConstraint  name="FixedConstraint" indices="@bbox.indices" />

            <Node name="Visual" >
                <MeshOBJLoader name="loader" filename="mesh/cylinder.obj" triangulate="true"/>
                <OglModel src="@loader" color="1.0 0.8 0.8"/>
                <BarycentricMapping  />
            </Node>
        </Node>
    </Node>
</Node>

Expected behavior
Drawing the hexahedric FEM and not crashing...