Error when calling onRemove if the creation failed

[gavinr]

Describe the bug

From @corrigancd in #140:

When a layer fails to load, even if the error is handled (#146), in our app there is a function which calls leafletMap.removeLayer to clear layers before re-adding them. This triggers the onRemove function in vectorTileLayer and map.removeLayer(this._mapboxGL) was called. The the problem was that this._mapboxGL was never initialized because the _createLayer function was exited early. So a check was added to make use that this.mapboxGL exists before calling remove.

Reproduction

tbd ... I'll try to follow up with this, or @corrigancd are you able to provide reproduction steps?

Logs

tbd

System Info

coming soon

Additional Information

Proposed solution from @corrigancd in #140: https://github.com/Esri/esri-leaflet-vector/pull/140/files#diff-d87a7a0181c4fb7f5a10b32e3494597f82c320b55306aa848df45d586513b30eR144-R146