GUI style can return negative int32 value for get_color(), but color only accepts uint32,

@blep: GUI style can return negative int32 value for get_color(), but color only accepts uint32, forcing a dirty work-around:

```
# PORT: "0xffff_ffff &" is a work-around for converting the negative int32 to uint32
rl.clear_background(rl.get_color(0xffff_ffff & rl.gui_get_style(rl.DEFAULT, rl.BACKGROUND_COLOR)))
```

