Reject clan invites when IsBotAccount

Also make it possible for quite rare situation of ASF accepting invite to SteamMasterClanID if it couldn't join due to group being non-public

ArchiSteamFarm/ArchiHandler.cs

@@ -29,6 +29,7 @@ using System.IO;
 using System.Linq;
 using System.Net;
 using System.Threading.Tasks;
+using ArchiSteamFarm.CMsgs;
 using SteamKit2;
 using SteamKit2.Internal;
 
@@ -212,6 +213,24 @@ namespace ArchiSteamFarm {
 			}
 		}
 
+		internal void AcceptClanInvite(ulong clanID, bool accept) {
+			if (clanID == 0) {
+				ArchiLogger.LogNullError(nameof(clanID));
+				return;
+			}
+
+			if (!Client.IsConnected) {
+				return;
+			}
+
+			ClientMsg<CMsgClientClanInviteAction> request = new ClientMsg<CMsgClientClanInviteAction>();
+
+			request.Body.ClanID = clanID;
+			request.Body.AcceptInvite = accept;
+
+			Client.Send(request);
+		}
+
 		private void HandleFSOfflineMessageNotification(IPacketMsg packetMsg) {
 			if (packetMsg == null) {
 				ArchiLogger.LogNullError(nameof(packetMsg));