Fix null pointer dereference in echo-message

The bug was introduced while fixing #1705. If a client did not enable
echo-message, and doesn't have a network, it crashes.

Thanks to LunarBNC for reporting this

src/Client.cpp

@@ -889,7 +889,7 @@ void CClient::EchoMessage(const CMessage& Message) {
     CMessage EchoedMessage = Message;
     for (CClient* pClient : GetClients()) {
         if (pClient->HasEchoMessage() ||
-            (pClient != this && (m_pNetwork->IsChan(Message.GetParam(0)) ||
+            (pClient != this && ((m_pNetwork && m_pNetwork->IsChan(Message.GetParam(0))) ||
                                  pClient->HasSelfMessage()))) {
             EchoedMessage.SetNick(GetNickMask());
             pClient->PutClient(EchoedMessage);