text: Title: M.layers.annotation.polygons[0].data - IndexError: list index out of range
  Body: When I run 3rd cell from 
  
  https://github.com/OpenGeoscience/geonotebook/blob/master/notebooks/04_Annotations.ipynb
  
  d, n = next(M.layers.annotation.polygons[0].data)
  
  I receive:
  ---------------------------------------------------------------------------
  IndexError                                Traceback (most recent call last)
  <ipython-input-11-66a9995560d8> in <module>()
  ----> 1 d, n = next(M.layers.annotation.polygons[0].data)
        2 #d, n = next(M.layers.annotation.rectangles[1].data)
  
  IndexError: list index out of range