Window.set_on_close page

[DanRathbun]

WebDialog.set_on_close page would be helpful to warn of double calling (at least in SU 2016 on Windows.)

Ref ... UI::WebDialog set_on_close block is called twice

[thomthom]

I've not been able to reproduce that. (See linked issue.)

[DanRathbun]

This was actually a circular code call. (Programmer error!) The LM should warn not to call close() from within the set_on_close() block or any code that it calls.

Ie, the API docs are not clear that the window is still visible, and will not actually be destroyed until the block finishes and set_on_close() returns.