Incorrect error message in fillGradientAngular function

There is a mismatch between the validation check and the error message in the `fillGradientAngular()`

```nim
if paint.gradientHandlePositions.len != 3:
    raise newException(PixieError, "Angular gradient requires 2 handles")
```

The code validates that gradientHandlePositions.len must equal 3
But the error message states "requires 2 handles"