If dragging a VertexControl while modifying the graph, UpdateVertexEdges would be called for an control without Vertex and RootArea and thus throwing and GX_InvalidDataException. Edges should not be updated for a VertexControl lacking a Vertex.
Merge pull request #5 from stefanpe/DragCrashFix

UpdateVertexEdges throws exception when trying to update VertextControl without Vertex