Fillet causes crash on Mac

Using the following code:

`import cadquery as cq

cylinder = cq.Workplane("XY" ).circle(54.5).extrude(20)

torus = cq.Solid.makeTorus(
32, 14,
pnt=cq.Vector(0,0,20),
dir=cq.Vector(0,0,1),
angleDegrees1=0,
angleDegrees2=360
)
lid = cylinder.cut(torus)
lid = lid.edges(">Z").fillet(1.0)
`

I get the following crash on MacOS 10.15.4:

`python(39157,0x1154efdc0) malloc: *** error for object 0x7fbc42c7d6b8: pointer being freed was not allocated
python(39157,0x1154efdc0) malloc: *** set a breakpoint in malloc_error_break to debug`

This is using everything installed from conda:
- cadquery: 2.0
- cq-editor: master (as of 2020-05-05)
- pythonocc-core: 0.18.2
- Python: 3.7.4