[comctl32] Fix SEGV in file dialogs (bug 3366)

[Troy Rollo]

On Wed, 12 Oct 2005 06:05, Alexandre Julliard wrote:
> I think it would be a lot cleaner to put the IsWindow test in the
> notify functions and make them return FALSE (or some appropriate code)
> when the window is destroyed. Then all you have to do in the callers
> is check the result instead of duplicating the IsWindow calls all over
> the place.

In most cases this would work, but there are a few cases where a value 
returned from the callback is used or tested for something else, including 
one where a return is made if the return value is !FALSE and not if it is 
FALSE, and one where execution should continue regardless of the return value 
of the notification. The latter is more problematic since it would require 
either some magic value that we hope the app does not return or a different 
notification function that does not interfere with the value returned by the 
application.