nsh: fix nsh redirect fd double close

[Frozen935]

avoid double-close of redirection fds

Summary

Fix a double close() in foreground redirection. nsh_undirect() already closes the redirected fd_in/fd_out, but close_redir would close them again. Reset fd_in/fd_out to -1 after nsh_undirect() to avoid closing the same fd twice.

Impact

nsh_redirect.

Testing

# NSH Script
echo "start" > /tmp/test.log
help >> /tmp/test.log
cat < /tmp/test.log