This bug was initially filed as mapbox/mapbox-gl-js#7019 but I'm moving it here because the bug is in the plugin.

When you change a map's style, the route feature is removed causing this line to throw the error Error: The layer 'directions-route-line-alt' does not exist in the map's style and cannot be queried for features.

Steps to Trigger Behavior

1. Add directions route to map
2. Change base map style
3. Move mouse around the map

Link to Demonstration

https://plnkr.co/edit/M8mj1WTH1KjDa1dhiUKw?p=preview

Expected Behavior

The plugin should be able to handle this situation so that no errors are thrown.

Actual Behavior

Errors are thrown.

cc @mikeomeara1