3D Printer Extruder Support Example Broken In CQ 2.0

It looks like [this example](https://github.com/CadQuery/cadquery-contrib/blob/master/examples/3D_Printer_Extruder_Support.py) was broken in the transition to PythonOCC. It fails in both CQ-editor and the jupyter_cadquery extension. Here's a jupyter_lab stack trace from this issue: https://github.com/bernhard-42/jupyter-cadquery/pull/8
```
IndexError Traceback (most recent call last)
in
141 # add reinforcement holes
142 cutout_rad -= 2*cutout_offset
--> 143 res = res.faces('>Z').workplane().\
144 pushPoints([(-cutout_rad, -main_plate_thickness/4),
145 (cutout_rad, -main_plate_thickness/4)]).\
...
IndexError: list index out of range
```