Blender Git Loki

Bugfix #33159

Histogram in Blender was nearly useless - it just didnt work, showed
confusing blank results.

Two reasons for it:
- It was including Alpha in the weighted total value
(RGB images have alpha 255 for all pixels)
- It was counting the a total weight value max(R, G, B, A), instead of
using max(R) and max(G) etc.

Now it all draws much nicer - similar to Da Gimp! :)