IndexError thrown when finishing the annotation

[ygorg]

Thank you for introducing a back button !!

• Buttons are not updated when reaching the end of the annotation.
• Buttons are re-enabled when going back from the end.

How to reproduce :

from pigeon import annotate
annotations = annotate(
  ['I love this movie', 'I was really disappointed by the book'],
  options=['positive', 'negative']
)

[csaroff]

Thanks for the contribution!