stop KeyNotFoundException() being thrown in RemoveScenePresence if the agent isn't present in the presence dictionary
stop KeyNotFoundException() being thrown in RemoveScenePresence if the agent isn't present in the presence dictionary

the code to do this was there but was being circumvented by newmap[agentID] before the check actually took place

cdbean/CySim,cdbean/CySim,cdbean/CySim,cdbean/CySim,cdbean/CySim,cdbean/CySim