Cursor does not hide

When playing a video in full screen mode the cursor / mouse pointer does not automatically hide anymore. It is a bit annoying and also it is not good for OLED screen when watching something long duration.

```
Linux 5.4.6-2-MANJARO #1 SMP PREEMPT 2019 x86_64 GNU/Linux
qtwebflix 0.1-179-g1596524
KDE Framework 5.65.0
Plasma 5.17.4
Qt 5.14.0
```

