[AD] [WIN] Tentative fix for the close button bug

[Eric B. <ebo...@li...>]

Encouraged by Peter's effort to fix the equivalent problem under Unix,
I finally sat down and started fiddling with the code. The attached patch
is a first result.

It works on my system, but I've never come across the aforementioned bug.

--
Eric Botcazou
ebo...@mu...