fixed bug in removing contacts from a conversation

Ignore-this: 1e0142ea90c3533957d3c605b27b2aa1

If a conversation had more than 2 people and one of those people went offline, you could
not add another person to the conversation.

darcs-hash:20141027222550-c21fe-188b0f397e4e9171142cbecdbecadea795f96658