Change next to text in Item 16

[atwalsh]

Updated index_words in Item 16 by changing changing next to text. Before this change, index_words would return [0] for an empty string.

Better-Python-59-Ways/item_16_generators_instead_of_lists.py

Line 13 in 9eaaba2

if next:

index_words_iter returns an empty list when text is an empty string which I assume is the intended result.