The problem addressed here is that there was no mean to check if an iterator
points the last of the elements being iterated over. Such checking is necessary
to reliably dereference the iterator (i.e., calling the operator*() method of the
underlying C++ iterator object).
Now Interface0DIterator and StrokeVertexIterator have an .at_last property
to check if an iterator points the last element. Using this new API feature,
the present commit partly reverts the previous commit rBeb8964fb7f19 to
better address T41464.
Differential revision: https://developer.blender.org/D752
Author: flokkievids (Folkert de Vries)
Reviewed by: kjym3 (Tamito Kajiyama)
f6b4b12961