Fix bar levels when shown less than 512

[KRtekTM]

Fix for FFTControl2 showing just 16 bars

[KRtekTM]

bug: https://youtu.be/sah4bLztEg4
Video from fix test here: https://www.youtube.com/watch?v=LSGSYBV7mA8

[franck-gaspoz]

sorry i didn't see you pr before.. today! i can't figure out what your change purpose is (if you are still here you could give a bit of explanations). your bug report is so nice! wow what an ui you have done :), however it seems to be a good fix. i check on my side and give you a feedback as soon it is done

[KRtekTM]

Thanks a lot. As I'm using my application every day, I'm less and less sure that the fix is right, or that there is a bug in the smaller spectrum bar viewer.
However I think there is a problem with the larger one (at the bottom). As they share the logic to render, I was not able to properly fix it, so what is now in my repository is "just fine", but I'm not happy with it.
It looks like some kind of issue when showing more than 512 bars or something like that.

For the small one, which was the PR about, I adjusted the bars (and their labels) according to what I can see in classic Winamp and it looks like your approach was right but I was not looking inside the code for a while, so now I'm trying to refresh my memory :D

Also really thanks for the project. I'm using the application I'm building around it with this screen https://www.waveshare.com/product/7.9inch-hdmi-lcd.htm so it now has touch capability etc.