Occasional crash when AI wins online

[andreybutenko]

TypeError: Cannot read property 'length' of undefined
    at Object.nextTurn (/srv/node/playuno.app/common/Uno.js:126:47)
    at Object.playCard (/srv/node/playuno.app/common/Uno.js:60:12)
    at chooseCard (/srv/node/playuno.app/server/models/Match.js:92:15)
    at Timeout.setTimeout [as _onTimeout] (/srv/node/playuno.app/common/AiPlayer.js:25:24)
    at ontimeout (timers.js:427:11)
    at tryOnTimeout (timers.js:289:5)
    at listOnTimeout (timers.js:252:5)
    at Timer.processTimers (timers.js:212:10)