After entering draw_point mode with no features, getAll() returns a Point with no coordinates

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**mapbox-gl-js version**: 0.44.2
**mapbox-gl-draw version**: 1.0.7

### Steps to Trigger Behavior

Do something like this:

```
map.addControl(draw);
draw.set({type: 'FeatureCollection', features: []});
draw.changeMode('draw_point');
console.log(draw.getAll());
```

jsbin: https://jsbin.com/hecipexiju/1/edit?html,output

### Expected Behavior

I would have expected `draw.getAll()` to return an empty `FeatureCollection`.

### Actual Behavior

I get a `FeatureCollection` with one feature, which is a `Point` with an empty array as `coordinates`, which is invalid GeoJSON. I have to manually filter such points out of the object before passing them downstream, otherwise calculations fail.

Start by reproducing the issue with the draw.set and draw.changeMode('draw_point') calls shown in the report, then trace the draw_point mode and draw.getAll() entry points. Confirm that an empty drawing returns an empty FeatureCollection rather than a Point with empty coordinates, and add or update coverage if the repository has relevant tests.

Written by the indexing model from the issue text.