fix for FontLab Dialog.GetValue() returning the wrong selected list inde...

I have pulled a similar request on Robofab's Github:
<https://github.com/robofab-developers/robofab/pull/14>

Basically, since FontLab 5.2, the built-in dialog's GetValue() method return a wrong index value for the selected list item. Without a patch, all List dialogs in dialogKit are broken when using FontLab 5.2.
In that other thread, Adam Twardoch says they are not planning to fix this, so I think you'll need to fix it from your end.

All best, 

Cosimo