TreeView assert in selectionForRowRange

An assert makes the application crash with TreeView and with extended selection.

Steps for reproduce:

• Start the filesystem TreeView example
• Click on the expand arrow of a root node
• Select a contiguous range of children of expanded node (without the root node)
• Click on the expand arrow of the root node for collapsing it
• The selection should disappear
• Click on the root node label
• Crash