Draft: Possibly fix saving EXR files with extremely low alpha values

It seems like Krita may leave garbage in the color channels of EXR files with "almost zero" alpha channel value. It will cause artifacts to appear on the next loading.

Hence, when saving pixels with very low alpha value we should just reset all color and alpha channels to avoid these artifacts on further loading.

Bug report from KA: https://krita-artists.org/t/exr-layer-fringe/103226