Overlay breaks if the top window does not fit on the screen

[marienz]

The attached example, ran in urwid 0.9.9, breaks with:

AssertionError?: top canvas of overlay not the size expected!(10, 0, -6, 10)

if the terminal window it runs in is resized until the top window does not fit in it. It should probably just truncate the top window instead.

[marienz]

Inlining the failing example because trac does not let me attach a file (Permission denied for /var/local/trac/urwid/attachments/ticket/67...):

import urwid


def main(wrap=True):
    btext = urwid.Text('background ' * 100)
    ftext = urwid.Text('foreground ' * 100)
    python = urwid.PythonLogo()
    if wrap:
        ftext = urwid.LineBox(ftext)
    overlay = urwid.Overlay(ftext, urwid.Filler(btext),
                            'center', ('relative', 100),
                            'middle', None)
    mainloop = urwid.MainLoop(overlay)
    mainloop.run()


if __name__ == '__main__':
    main()