Transparent pixels affected by brightness contrast

[audiority]

Hi,
we noticed that when applying brightness/contrast to a ARGB image, the transparent pixels becomes opaque someways.

Original:

With brightness/contrast

You can clearly see the "box" around the knob, which is not desired.

[asimilon]

This seems to be in the same class of issue as a fix I made that @FigBug merged back in 2019 : #7

This should be able to be applied similarly to any other affected methods?