C4NetIOUDP: Fix sending data before ConnOK

With my fix from 9eb2478b2 ("C4NetIOUDP: Fix timeout during non-MC
connection"), C4NetIOUDP would send data packets to the master server
before the ConnOK packet. The server would then discard these data
packets, resulting in a one-second delay until retransmission.

src/network/C4NetIO.cpp

@@ -3259,6 +3259,7 @@ void C4NetIOUDP::Peer::OnRecv(const C4NetIOPacket &rPacket) // (mt-safe)
 		}
 		// build ConnOk Packet
 		ConnOKPacket nPack;
+		bool fullyConnected = false;
 
 		nPack.StatusByte = IPID_ConnOK; // (always du, no mc experiments here)
 		nPack.Nr = fBroadcasted ? pParent->iOPacketCounter : iOPacketCounter;
@@ -3271,10 +3272,12 @@ void C4NetIOUDP::Peer::OnRecv(const C4NetIOPacket &rPacket) // (mt-safe)
 		{
 			nPack.MCMode = ConnOKPacket::MCM_NoMC; // du ok
 			// no multicast => we're fully connected now
-			OnConn();
+			fullyConnected = true;
 		}
 		// send it
 		SendDirect(C4NetIOPacket(&nPack, sizeof(nPack), false, addr));
+		// Clients will try sending data from OnConn, so send ConnOK before that.
+		if (fullyConnected) OnConn();
 	}
 	break;