riched20: new selection invalidation logic

[Krzysztof Foltman]

Vitaliy Margolen wrote:

> I don't see how that can be if users report crashes immediately when installer
> tries to show licence. Or when user tries to scroll text to the bottom so "Next"
> button will become enabled.

It doesn't happen on my machine on installers I've tried (including the 
infamous NSIS), so it's not because of lack of testing at all. In fact, 
I still don't know why it happens on one machine and not another.

>> Anyway, the issue is not easy to solve, so I'd be grateful for any ideas 
>> that may help in solving this important issue.
> _TRY
> {
>   call riched20
>  }
> _EXCEPT(handler)
> _ENDTRY
> Seems like easy to me.

How does that solve the improper operation vs lack of bug reports issue? 
Do we want to have buggy richedit forever?

Unless you put some mail sending code in the exception handler. But that 
qualifies as spyware and shouldn't happen.

Krzysztof