correct possible null reference during disconnectPeer callback;

src/fne/network/TrafficNetwork.cpp

@@ -2282,7 +2282,10 @@ void TrafficNetwork::erasePeer(uint32_t peerId)
     {
         auto it = std::find_if(m_peers.begin(), m_peers.end(), [&](PeerMapPair x) { return x.first == peerId; });
         if (it != m_peers.end()) {
-            neighborFNE = it->second->peerClass() == PEER_CONN_CLASS_NEIGHBOR;
+            FNEPeerConnection* conn = it->second;
+            if (conn != nullptr) {
+                neighborFNE = conn->peerClass() == PEER_CONN_CLASS_NEIGHBOR;
+            }
             m_peers.erase(peerId);
         }
     }