FolderItem.ShowModal() crashes the IDE

<https://xojo.com/issue/25825>
As it occured with Xojo, I set this auto-generated case as ‘private’. But the crash also occurs with 2012r2.1, so obviously it’s not beta related.

I know, I know… I shouldn’t code until completely awaken…
This crash begs one question, though: Is the FolderItemDialog meant to be instantiated?
If not, there should be a clear mention of this in the doc.

FolderItemDialog is meant to be an abstract base class and not instantiated directly. It probably should have its constructor made private.