Incorrect hsl properties for rgb colors

QML colors made using hex triplets or with `Qt.rgba` have incorrect hsl properties.

For example, both `#ffffff` and `Qt.rgba(1, 1, 1, 1)`, have an incorrect hue of -1 and a saturation of 0. Instead of the expected hue of 0 and saturation of 1.
The same color constructed using `Qt.hsla(1, 1, 1, 1)` has a correct hue of 0, a saturation of 1 and a lightness of 1.
This is shown in the provided minimal test project.

The r, g and b properties are still correct and can be used to manually convert the color to other models.