Fixed hotspot of hand-cursor

It's a small thing but it was bugging me for as long as i knew LMMS. The cursor was three pixels off, creating a weird feeling when composing beatlines.

The position of the cursor in this image still caused the first 1/16-beat to be toggled, despite the finger clearly points on the second 1/16-beat.

![screenshot of bb editor](https://imgur.com/rJtS2Uw.png)

With the fix, the cursor's hotspot is exactly at the tip of the finger.