bug with function EditableGeoJsonLayer.getCursor()

[linze99]

after deck.gl update to 8.8.0+,my propram raise a exception like this: it happend in the function EditableGeoJsonLayer.getCursor(), at the mean time this.state is undefined but not null;

after changed the code with:

  if (this.state === null || this.state === undefined) {
    // Layer in 'Awaiting state'
    return null;
  }

it works fine