Reacting with 🎟️ if already in audience list throws silent error

[kepler471]

It seems that if a user uses the 🎟️ reaction on a bot message after they have already been added to the list, there is no response in the channel, but this error occurs:

 Ignoring exception in on_reaction_add
Traceback (most recent call last):
  File "/home/steli/.pyenv/versions/film-bot/lib/python3.6/site-packages/discord/client.py", line 312, in _run_event
    await coro(*args, **kwargs)
  File "/home/steli/source/film_night_discord_bot/your_bot.py", line 111, in on_reaction_add
    await common_reaction_handler(reaction, user)
  File "/home/steli/source/film_night_discord_bot/your_bot.py", line 97, in common_reaction_handler
    await handlers.handle_reaction(reaction, user, client)
  File "/home/steli/source/film_night_discord_bot/handlers.py", line 34, in handle_reaction
    cmd_obj = COMMAND_HANDLERS[mapping[str(reaction.emoji)]]
KeyError: '🎟️'
Temporary user set as  Wattsit#0001
Temporary user set as  None
Temporary user set as  Wattsit#0001
reaction call Wattsit
reaction call Direct Message with Wattsit#0001
Temporary user set as  None

We want the bot to message the channel that the user alreay has a ticket, which was previously working.