LayoutHelpers.CalculateLayout() crashes with OverlapRemovalMethod set to Prism

On this configuration

    Microsoft.Msagl.Layout.MDS.MdsLayoutSettings msaglMdsLayoutSettings= new Microsoft.Msagl.Layout.MDS.MdsLayoutSettings();        
    msaglMdsLayoutSettings.EdgeRoutingSettings.EdgeRoutingMode = Microsoft.Msagl.Core.Routing.EdgeRoutingMode.StraightLine;
    msaglMdsLayoutSettings.NodeSeparation = 0.05f;
    msaglMdsLayoutSettings.ScaleX = 5.0f;
    msaglMdsLayoutSettings.ScaleY = 5.0f;
    msaglMdsLayoutSettings.RemoveOverlaps = true;
    msaglMdsLayoutSettings.OverlapRemovalMethod = Microsoft.Msagl.Core.Layout.ProximityOverlapRemoval.MinimumSpanningTree.OverlapRemovalMethod.Prism;

When the nodes are added to the graph but there are no edges connected to them which are not added. Then we draw the layout it crashes.

An example:

    Node a = new Node(CurveFactory.CreateRectangle(0.05f, 0.05f, new Microsoft.Msagl.Core.Geometry.Point()), "a");
    Node b = new Node(CurveFactory.CreateRectangle(0.05f, 0.05f, new Microsoft.Msagl.Core.Geometry.Point()), "b");
    Node c = new Node(CurveFactory.CreateRectangle(0.05f, 0.05f, new Microsoft.Msagl.Core.Geometry.Point()), "c");
    msaglGraph.Nodes.Add(a);
    msaglGraph.Nodes.Add(b);
    msaglGraph.Nodes.Add(c);
    Edge e1 = new Edge(a, b);
    msaglGraph.Edges.Add(e1);

That example crashes because there is a node c which isn't connected by any edges. Anyone know if this is a bug?

Start by reproducing the provided three-node example with MdsLayoutSettings, Prism overlap removal, and one unconnected node. Trace LayoutHelpers.CalculateLayout() to identify the crash, then verify that the same configuration completes without crashing and includes the disconnected node in the layout.