Clean up a stale foreign handle in winnps.c.

Clean up a stale foreign handle in winnps.c.

I had set up an event object for signalling incoming connections to
the named pipe, and then called handle_add_foreign_event to get that
event object watched for connections - but when I closed down the
listening pipe, I deleted the event object without also cancelling
that foreign-event handle, so that winhandl.c would potentially call
the callback for a destroyed object.

(cherry picked from commit 6f241cef2c9770abf71349dd59547b3e5b4c0301)