Optionals with '*' should accept a defaultValue

JS argparse fails the test_argparse.py test for TestOptionalsNargsZeroOrMore(ParserTestCase
Tests specifying an args for an Optional that accepts zero or more

In this case ['-y'] with nargs='*' and defaultValue= 'spam', should be
using that default.  (Positionals with '*' on the other hand don't)

Correction: test for optionStrings.length in ArgumentParser._getValues()
Action.isPositional() does the same thing.