Multicast chat messages

Only the sender and the recipients receive the chat messages.
This commit only has an affecto on messages where the addressee(s) are
selected through the dropdown. Addressee(s) selected with a "/" command
are still sent to evevyone and filteret by the receiver.

source/network/NetClient.cpp

@@ -465,10 +465,17 @@ void CNetClient::SendAssignPlayerMessage(const int playerID, const CStr& guid)
 	SendMessage(&assignPlayer);
 }
 
-void CNetClient::SendChatMessage(const std::wstring& text)
+void CNetClient::SendChatMessage(const std::wstring& text,
+	std::optional<std::vector<std::string>> receivers)
 {
 	CChatMessage chat;
 	chat.m_Message = text;
+	if (receivers)
+		std::transform(receivers->begin(), receivers->end(), std::back_inserter(chat.m_Receivers),
+			[](std::string& receiver)
+			{
+				return CChatMessage::S_m_Receivers{std::move(receiver)};
+			});
 	SendMessage(&chat);
 }
 
@@ -732,7 +739,7 @@ bool CNetClient::OnChat(CNetClient* client, CFsmEvent* event)
 
 	client->PushGuiMessage(
 		"type", "chat",
-		"guid", message->m_GUID,
+		"guid", message->m_SenderGUID,
 		"text", message->m_Message);
 
 	return true;