`fill` can overflow the call stack and crash the app
repro:

```python
import pyxel

def update():
    ...

def draw():
    pyxel.fill(0, 0, 7)

def main():
    pyxel.init(256, 256, "fill")
    pyxel.run(update, draw)


if __name__ == "__main__":
    main()
```

this crashes on my machine.

i've put a possible fix in #614