w32: Don't use CloseHandle on an arbitrary integer.

* src/assuan-support.c (my_waitpid): Do not close the PID = it is not
a handle.

At some time in the distant past we might have used the process object
as pid which obviously required a close. However this was changed and
so what we did here was to close an arbitrary handle (one which
matches the pid).

• GnuPG-bug-id: T4237
• Signed-off-by: Werner Koch <wk@gnupg.org>