Moving event from PM to public stream crashes RSVPBot

[alexandrinaw]

I was playing around with RSVPBot locally trying to learn about how it works when you PM it and found a way to crash the bot.

Steps to reproduce:

1. rsvp init in a PM with RSVPBot
2. rsvp move <any stream/topic>

Questions:

1. Should users be able to initialize events in a PM and then move them? Sometimes interacting with RSVPBot is kind of noisy, so it seems like it might be a nice feature to set up the event privately and then move it to another stream. But it's also weird that you can even create an event in a PM with RSVPBot, because if you don't move the event, you're the only person who can see it, which seems kind of pointless.
2. I guess I only had one question...

Anyway, there are multiple ways to fix this, but it'll depend on the answer to that question.

Here's the traceback:

Traceback (most recent call last):
  File "bot.py", line 108, in <module>
    new_bot.main()
  File "bot.py", line 83, in main
    self.client.call_on_each_message(lambda msg: self.respond(msg))
  File "/Users/alexwilson/.virtualenvs/rsvpbot/lib/python2.7/site-packages/zulip/__init__.py", line 308, in call_on_each_message
    self.call_on_each_event(event_callback, ['message'])
  File "/Users/alexwilson/.virtualenvs/rsvpbot/lib/python2.7/site-packages/zulip/__init__.py", line 301, in call_on_each_event
    callback(event)
  File "/Users/alexwilson/.virtualenvs/rsvpbot/lib/python2.7/site-packages/zulip/__init__.py", line 306, in event_callback
    callback(event['message'])
  File "bot.py", line 83, in <lambda>
    self.client.call_on_each_message(lambda msg: self.respond(msg))
  File "bot.py", line 63, in respond
    self.send_message(reply)
  File "bot.py", line 70, in send_message
    msg_to = msg['sender_email']
KeyError: 'sender_email'

[wtfcarlos]

Yup! That would be a great feature to add. See #37