If total is zero application crashes with CALayerInvalidGeometry

If total value is zero (in case there is not data yet) app crashes with message

```
Terminating app due to uncaught exception 'CALayerInvalidGeometry', reason: 'CALayer position contains NaN: [nan nan]'
```

Possible solution: ask delegate for UIView to show instead of Pie Chart or do something to prevent from dividing on zero
