fix segfault in channels impl eventmodel

channels/storage/impl.go

@@ -132,10 +132,12 @@ func (i *impl) UpdateFromUUID(uuid uint64, messageID *message.ID, timestamp *tim
 
 	msgToUpdate := &Message{
 		Id:     uuid,
-		MessageId: messageID.Marshal(),
 		Hidden: hidden,
 		Pinned: pinned,
 	}
+	if messageID != nil {
+		msgToUpdate.MessageId = messageID.Marshal()
+	}
 	if round != nil {
 		msgToUpdate.Round = uint64(round.ID)
 	}