Comment 3 for bug 1132053

You can indeed reproduce this as @radaiming said.
This fix I wrote seems to work:

if self.focusloc[1] < len(wlessL):
    self.wlessLB.set_focus(self.focusloc[1])
else:
    self.wlessLB.set_focus(len(wlessL) - 1)

or as @radaiming would do it

self.wlessLB.set_focus(min(self.focusloc[1], len(wlessL) - 1))