Arcs aren't drawn correctly on Windows 10, if sweep is negative

Positive sweeps:


But when changing drawtests.c as below...

```Diff
@@ -161,7 +161,7 @@ static void drawArcs(uiAreaDrawParams *p)

path = uiDrawNewPath(uiDrawFillModeWinding);

- add = (2.0 * uiPi) / 12;
+ add = -(2.0 * uiPi) / 12;

x = start + rad;
y = start + rad;
```

...we get negative sweeps resulting in this:


Same change on Linux:


Start with drawtests.c and reproduce the arc example on Windows 10 using the negative value for add, then compare it with the Linux result. Trace the libui drawing path used by the test and identify where negative sweeps are rendered differently; done means the negative-sweep arcs match the expected Linux behavior on Windows.

Written by the indexing model from the issue text.