Fancy UI can break while accumulating output

[vector-of-bool]

C:\Users\Colby\AppData\Local\pypoetry\Cache\virtualenvs\...-py3.9\lib\site-packages\dagon\event\event.py:78: UserWarning: An event handler function raised an exception. It has been ignored. Traceback (most recent call last):
  File "C:\Users\Colby\AppData\Local\pypoetry\Cache\virtualenvs\...-py3.9\lib\site-packages\dagon\event\event.py", line 75, in emit
    h(value)
  File "C:\Users\Colby\AppData\Local\pypoetry\Cache\virtualenvs\...-py3.9\lib\site-packages\dagon\ui\fancy.py", line 307, in _on_message
    self._append_message(msg)
  File "C:\Users\Colby\AppData\Local\pypoetry\Cache\virtualenvs\...-py3.9\lib\site-packages\dagon\ui\fancy.py", line 294, in _append_message
    self._pending_output += text + '\n'
TypeError: unsupported operand type(s) for +: 'method' and 'str'


  warnings.warn(f'An event handler function raised an exception. It has been ignored. {tb}')