Check if 'hero' exists in arena in 'attack' command in '__init__.py' main()

[fishroot]

> Orc killed Hero.
Hero is removed from arena.
Fight stopped!
Hero is dead. Monsters win!
attack dragon
Traceback (most recent call last):
  File "C:\ProgramData\Anaconda3\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\ProgramData\Anaconda3\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\ProgramData\Anaconda3\Scripts\conslayer.exe\__main__.py", line 7, in <module>
  File "C:\ProgramData\Anaconda3\lib\site-packages\conslayer\__init__.py", line 61, in main
    arena["hero"].attack(command[7:].strip())
  File "C:\ProgramData\Anaconda3\lib\site-packages\conslayer\arena.py", line 89, in __getitem__
    return self.__registry[name]