[3.12] gh-59317: Improve parsing optional positional arguments in argparse (GH-124303) (GH-124437)

Fix parsing positional argument with nargs equal to '?' or '*' if it is
preceded by an option and another positional argument.
(cherry picked from commit 4a5e4aade420c594c5b3fe0589e9e6b444bd6ee5)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>