Comment 8 for bug 627106

Calling self.scrollbar.set_value triggers an automatic call to on_scroll, which in turn calls handle_scroll, so there is no need to call handle_scroll again after calling self.scrollbar.set_value.

My branch https://code.launchpad.net/~mhall119/gwibber/keyboard-control-622677-try2/+merge/39420 already has a fix for this, by setting len(self.messages) as the upper bounds for the scroll value, and 0 for the lower bound, and removing the redundant call to handle_scroll.