Prevent division by zero in HWBA to HSVA conversions

[ickshonpe]

Problem

Division by zero in crates/bevy_color/src/hsva.rs when blackness is 1:

impl From<Hwba> for Hsva {
    fn from(
        Hwba {
            hue,
            whiteness,
            blackness,
            alpha,
        }: Hwba,
    ) -> Self {
        // Based on https://en.wikipedia.org/wiki/HWB_color_model#Conversion
        let value = 1. - blackness;
        let saturation = 1. - (whiteness / value);

        Hsva::new(hue, saturation, value, alpha)
    }
}

Solution

With Hsva colors if the value component is set to 0. the output will be pure black regardless of the values of the hue or saturation components.

So if value is 0, we don't need to calculate a saturation value and can just set it to 0:

impl From<Hwba> for Hsva {
    fn from(
        Hwba {
            hue,
            whiteness,
            blackness,
            alpha,
        }: Hwba,
    ) -> Self {
        // Based on https://en.wikipedia.org/wiki/HWB_color_model#Conversion
        let value = 1. - blackness;
        let saturation = if value != 0. {
            1. - (whiteness / value)
        } else {
            0.
        };

        Hsva::new(hue, saturation, value, alpha)
    }
}

[Bergerserkkeri]

Seems good to me