Refactor? call to _do_the_update in _do_update for length 1

[mconlon17]

In _do_update, if length 1 path, _do_the_update is called. seems that this call should follow the pattern seen in _do_two_step_update where the predicate is checked for cardinality and then _do_the_update is either called once for multiple values, or many times for multiple predicates. As is, path length 1 appears to handle only single predicate, multi-valued, not multi-predicate, single-valued. No "bug" example yet, but perhaps one could be created.