[net processing] Add Orphanage empty consistency check

When removing the final peer, assert that m_tx_orphanage is empty.

src/net_processing.cpp

@@ -1194,6 +1194,7 @@ void PeerManagerImpl::FinalizeNode(const CNode& node)
         assert(m_outbound_peers_with_protect_from_disconnect == 0);
         assert(m_wtxid_relay_peers == 0);
         assert(m_txrequest.Size() == 0);
+        assert(m_orphanage.Size() == 0);
     }
     } // cs_main
     if (node.fSuccessfullyConnected && misbehavior == 0 &&