Fix for crash when the message has a null user.  Problem experienced with HipChat adapter.
Fix for crash when the message has a null user.  Problem experienced with HipChat adapter.

/opt/hubot/node_modules/hubot-scripts/src/scripts/conversation.coffee:13
      if (robot.eatListeners[message.user.id] != null) {
                                         ^
TypeError: Cannot read property 'id' of undefined
    at Robot.receive (/opt/hubot/node_modules/hubot-scripts/src/scripts/conversation.coffee:13:42)
    at Robot.origReceive (/opt/hubot/node_modules/hubot/src/robot.coffee:120:21)
    at Robot.receive (/opt/hubot/node_modules/hubot-scripts/src/scripts/conversation.coffee:21:20)
    at HipChat.receive (/opt/hubot/node_modules/hubot/src/adapter.coffee:44:25)
    at Bot.<anonymous> (/opt/hubot/node_modules/hubot-hipchat/src/hipchat.coffee:127:21)
    at Bot.emit (events.js:77:17)
    at Bot.<anonymous> (/opt/hubot/node_modules/hubot-hipchat/node_modules/wobot/lib/bot.js:108:12)
    at Client.<anonymous> (native)
    at Client.emit (events.js:67:17)
    at Client.onRawStanza (/opt/hubot/node_modules/hubot-hipchat/node_modules/wobot/node_modules/node-xmpp/lib/xmpp/client.js:159:14)
josephcarmello/hubot-scripts,sklise/hubot-scripts,n0mer/hubot-scripts,arcaartem/hubot-scripts,wsoula/hubot-scripts,dbkaplun/hubot-scripts,markstory/hubot-scripts,iilab/hubot-scripts,alexhouse/hubot-scripts,phillipalexander/hubot-scripts,dhfromkorea/hubot-scripts,GrimDerp/hubot-scripts,justinwoo/hubot-scripts,github/hubot-scripts,jan0sch/hubot-scripts,ambikads/hubot-scripts,1stdibs/hubot-scripts,amhorton/hubot-scripts,ryantomlinson/hubot-scripts,DataDog/hubot-scripts,fromonesrc/hubot-scripts,flores/hubot-scripts,DataDog/hubot-scripts,zecahnin/hubot-scripts,1000hz/hubot-scripts,Ev1l/hubot-scripts,flores/hubot-scripts,jankowiakmaria/hubot-scripts,contolini/hubot-scripts,MaxMEllon/hubot-scripts,cycomachead/hubot-scripts,Tyriont/hubot-scripts,marksie531/hubot-scripts,modulexcite/hubot-scripts,jhubert/hubot-scripts,yigitbey/hubot-scripts,azimman/hubot-scripts,gregburek/emojibot,chauffer/hubot-scripts,dyg2104/hubot-scripts,terryjbates/hubot-scripts,davidsulpy/hubot-scripts,opentable/hubot-scripts,jacobtomlinson/hubot-scripts,magicstone1412/hubot-scripts,ericjsilva/hubot-scripts