Sound audition is played even when editor minimized
The Pyxel music editor played a preview on mouse over
the sound number list even when the window is minimized.
(When place the mouse cursor in the same position in the window.)

**Screen capture**
[https://twitter.com/doc1oo/status/1297400538212925440](https://twitter.com/doc1oo/status/1297400538212925440)

**Environment**
Windows 10 1909 / Pyxel 1.4.1 / Python 3.8.5