Sweep along arc and radial line leads to non-manifold shapes

Best demonstrated with a bit of code and a screenshot. Green is good shape, red is bad shape. The only difference is in using `sweep(…, transition = "round")` (which works) and the default `sweep(…, transition = "right")` (which does not work as intended). The bad shape is just one example … when varying measures, the position of the workplane etc. you'll get very different non-manifold shapes, and it is not obvious how the inputs lead to the changes in output. (Maybe an OpenCascade CAD kernel issue?)

```python
from math import sin, cos, radians

hole_radius = 4.5
circum_radius = 10
height = 5
wall_thickness = 2

left_endpoint = [cos(radians(-135)) * circum_radius, sin(radians(-135)) * circum_radius]
right_endpoint = [cos(radians(-45)) * circum_radius, sin(radians(-45)) * circum_radius]
left_arcpoint = [cos(radians(-135)) * hole_radius, sin(radians(-135)) * hole_radius]
mid_arcpoint = [hole_radius, 0]
right_arcpoint = [ cos(radians(-45)) * hole_radius, sin(radians(-45)) * hole_radius]

path = (
cq
.Workplane("XY")
.moveTo(*left_endpoint)
.lineTo(*left_arcpoint)
.threePointArc(mid_arcpoint, right_arcpoint)
.lineTo(*right_endpoint)
.wire()
)

good_sweep = (
cq
.Workplane("XY")
.workplane(offset = 15)
.center(*left_endpoint)
.transformed(rotate = (90, -45, 0))
.rect(wall_thickness, height)
.sweep(path, transition = "round")
)

bad_sweep = (
cq
.Workplane("XY")
.center(*left_endpoint)
.transformed(rotate = (90, -45, 0))
.rect(wall_thickness, height)
.sweep(path, transition = "right") # Only difference to the good part is transition type.
)

show_object(path, name = "path")
show_object(good_sweep, name = "good sweep", options = {"color": "green"})
show_object(bad_sweep, name = "bad sweep", options = {"color": "red"})

```


I'm using CadQuery and CQ-editor installed from their master branches in early January 2021, using Conda.