Missing Mapbox access token for a Mapbox source does not trigger the map.on('error') event

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mapbox-gl@0.44.2:

### Steps to Trigger Behavior

1. Instantiate a map
2. Bind to the mapbox-gl on error event
3. Do not specify a Mapbox access token
4. Load a style JSON with a source pointed at a mapbox:// endpoint
5. Thrown error caught by console but does not trigger error event

### Expected Behavior

Mapbox auth errors should trigger the [map.on('error')](https://www.mapbox.com/mapbox-gl-js/api/#map.event:error) event similar to all other Mapbox errors.

### Actual Behavior

Error event not triggered - caught instead by console.

### Additional Notes

According to the [error event documentation](https://www.mapbox.com/mapbox-gl-js/api/#map.event:error), mapbox-gl should use the error event instead of throwing an error. A link to where the error is thrown in the code [src/util/mapbox.js](https://github.com/mapbox/mapbox-gl-js/blob/03680eb57489cf442f8c538141ea27c73d98d532/src/util/mapbox.js#L29).

Start with src/util/mapbox.js at the linked error location and reproduce the documented steps using a mapbox:// source without an access token. Trace how the authentication error is handled relative to map.on('error'). Done means the missing-token error triggers the map error event instead of only being caught by the console.

Written by the indexing model from the issue text.