Crash when moving last item to archive

When the list contains just one item, and this is moved to the archive, the application crashes.
test: create new file, add one task, press x, press X, Crash.
Traceback (most recent call last):
  File "/usr/bin/todotxt-machine", line 11, in <module>
    load_entry_point('todotxt-machine==2.2.2', 'console_scripts', 'todotxt-machine')()
  File "/usr/lib/python3.6/site-packages/todotxt_machine/cli.py", line 179, in main
    show_filter_panel)
  File "/usr/lib/python3.6/site-packages/todotxt_machine/urwid_ui.py", line 992, in main
    self.loop.run()
  File "/usr/lib/python3.6/site-packages/urwid/main_loop.py", line 278, in run
    self._run()
  File "/usr/lib/python3.6/site-packages/urwid/main_loop.py", line 376, in _run
    self.event_loop.run()
  File "/usr/lib/python3.6/site-packages/urwid/main_loop.py", line 682, in run
    self._loop()
  File "/usr/lib/python3.6/site-packages/urwid/main_loop.py", line 719, in _loop
    self._watch_files[fd]()
  File "/usr/lib/python3.6/site-packages/urwid/raw_display.py", line 393, in <lambda>
    event_loop, callback, self.get_available_raw_input())
  File "/usr/lib/python3.6/site-packages/urwid/raw_display.py", line 493, in parse_input
    callback(processed, processed_codes)
  File "/usr/lib/python3.6/site-packages/urwid/main_loop.py", line 403, in _update
    self.process_input(keys)
  File "/usr/lib/python3.6/site-packages/urwid/main_loop.py", line 509, in process_input
    something_handled |= bool(self.unhandled_input(k))
  File "/usr/lib/python3.6/site-packages/urwid/main_loop.py", line 555, in unhandled_input
    return self._unhandled_input(input)
  File "/usr/lib/python3.6/site-packages/todotxt_machine/urwid_ui.py", line 536, in keystroke
    self.archive_done_todos()
  File "/usr/lib/python3.6/site-packages/todotxt_machine/urwid_ui.py", line 452, in archive_done_todos
    self.move_selection_top()
  File "/usr/lib/python3.6/site-packages/todotxt_machine/urwid_ui.py", line 355, in move_selection_top
    self.listbox.set_focus(0)
  File "/usr/lib/python3.6/site-packages/urwid/listbox.py", line 562, in set_focus
    raise IndexError("Can't set focus, ListBox is empty")
IndexError: Can't set focus, ListBox is empty
^CException ignored in: <module 'threading' from '/usr/lib/python3.6/threading.py'>
Traceback (most recent call last):
  File "/usr/lib/python3.6/threading.py", line 1294, in _shutdown
    t.join()
  File "/usr/lib/python3.6/threading.py", line 1056, in join
    self._wait_for_tstate_lock()
  File "/usr/lib/python3.6/threading.py", line 1072, in _wait_for_tstate_lock
    elif lock.acquire(block, timeout):
KeyboardInterrupt
AnthonyDiGirolamo / todotxt-machine

Crash when moving last item to archive #49
