Crash when clearing a Shapes container by script while a shape is selected

[klayoutmatthias]

To reproduce:

• Create a layout with one layer 1/0
• Draw a box, select it
• In the console run

ly = pya.CellView.active().layout()
canvas = ly.top_cell().shapes(ly.layer(1, 0))
canvas.clear()

Effect: the application crashes