[FIXED] Access (read) violation using a LLVivoxVoiceClient::sessionState() after it's been free'ed

The shared pointer is passed by reference to LLVivoxVoiceClient::deleteSession() where
mSessionsByHandle.erase(iter) removes the last reference causing it to destruct while still
being accessed later on in the function.

indra/newview/llvoicevivox.cpp

@@ -5670,7 +5670,8 @@ void LLVivoxVoiceClient::deleteAllSessions()
 
     while (!mSessionsByHandle.empty())
 	{
-        deleteSession(mSessionsByHandle.begin()->second);
+        const sessionStatePtr_t session = mSessionsByHandle.begin()->second;
+        deleteSession(session);
 	}
 	
 }