Taskbar Volume Control - does not change by "step" size in Win10 Indicator

@m417z 
When "Volume indicator" style is set to `Win 10` , the  volume indicator only changes by  `2` step-size on mousewheel scroll. 

I've tried to look into at this line: https://github.com/ramensoftware/windhawk-mods/blob/c17ce99483d75133beaed805c705e10872660059/mods/taskbar-volume-control.wh.cpp#L1095
and tried to do smth in fork, but cant succeed. any hint?