CoBib TUI crashes when aborting quit

When aborting the quit command, the TUI crashes the following traceback:

Traceback (most recent call last):
  File "/usr/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/home/max/Git/cobib/cobib/__main__.py", line 128, in <module>
    main()
  File "/home/max/Git/cobib/cobib/__main__.py", line 80, in main
    tui()
  File "/home/max/Git/cobib/cobib/tui/__init__.py", line 16, in tui
    curses.wrapper(TUI)
  File "/usr/lib/python3.9/curses/__init__.py", line 94, in wrapper
    return func(stdscr, *args, **kwds)
  File "/home/max/Git/cobib/cobib/tui/tui.py", line 182, in __init__
    self.loop()
  File "/home/max/Git/cobib/cobib/tui/tui.py", line 364, in loop
    TUI.COMMANDS[cmd](self)
  File "/home/max/Git/cobib/cobib/tui/tui.py", line 63, in <lambda>
    'Quit': lambda self: self.quit(),
  File "/home/max/Git/cobib/cobib/tui/tui.py", line 243, in quit
    self.viewport.revert()
  File "/home/max/Git/cobib/cobib/tui/frame.py", line 48, in revert
    self.buffer, state = self.history.pop()
IndexError: pop from empty list