Infinite loop in traitsui.extras.demo

[ievacerny]

The tutorial application hangs when choosing an element that has a directory as a previous sibling. E.g. choosing sibling2 in this tree would freeze the application:

parent/
    sibling1/
        leaf.py
    sibling2/
        leaf.py

The application hangs because of this infinite loop:

traitsui/traitsui/extras/demo.py

Lines 963 to 967 in 3e2ce86

	if index > 0:
	previous = siblings[index - 1]
	previous_children = previous.tno_get_children(previous)
	while len(previous_children) > 0:
	previous = previous_children[-1]

[corranwebster]

The fix looks like it is simply adding

                    previous_children = previous.tno_get_children(previous)

after 967. The algorithm is basically looking for the previous element in a preorder tree traversal.