Validate GeoJSON

Nobody has claimed this yet.

**mapbox-gl-js version**: 0.39.1

Due to some sloppy code I passed some pretty defective GeoJSON, like:

```
{
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"coordinates": [145, -37]
}
]
}
```

Instead of raising a " Error: Input data is not a valid GeoJSON object." error, this error is thrown:

```
Error: TypeError: Cannot read property 'type' of undefined
at Actor.receive (mapbox-gl.js:397)
at e.whenMapLoaded ((index):58)
at e.Evented.fire (mapbox-gl.js:417)
at e._render (mapbox-gl.js:391)
```

Adding at least a `"geometry"` attribute to the `Feature` object triggers the correct error.

Start by reproducing the malformed FeatureCollection in the issue and follow the reported stack trace to Actor.receive in the mapbox-gl.js bundle. Confirm that a Feature missing geometry produces the intended invalid GeoJSON error rather than a TypeError; the issue is done when this case is handled consistently.

Written by the indexing model from the issue text.