Opening a stack changes it's set rect

[Paul Dupuis]

I discovered today that opening a stack changes its set rect (at least 
under Windows 10 in LC904/905rc1 when opening a stack invisible

See this little gem: https://quality.livecode.com/show_bug.cgi?id=22097

Not a problem is you are just popping up windows and then setting their 
positions, but if, for some reason, you want to precisely place windows 
(like we do) and then open them, this is a pain in the rear!

Opening a window/stack should not change its rect!