gui: consider obs in LayoutViewer::generateCutLayerMaximumSizes()
gui: consider obs in LayoutViewer::generateCutLayerMaximumSizes()

We can have a case where we have no vias or pins on a cut layer but do
have obs shapes.

Signed-off-by: Matt Liberty <44ef1ce0ef6935daf739a0795dad249ba5322e97@eng.ucsd.edu>

The-OpenROAD-Project/OpenROAD,QuantamHD/OpenROAD,The-OpenROAD-Project/OpenROAD,The-OpenROAD-Project/OpenROAD,QuantamHD/OpenROAD,QuantamHD/OpenROAD,The-OpenROAD-Project/OpenROAD,QuantamHD/OpenROAD,The-OpenROAD-Project/OpenROAD,QuantamHD/OpenROAD