Check for error before deferring to close resource

In case of error, returned resource is always nil.
Deference it only when call was successful

Closes #113

utils/utils.go

@@ -277,21 +277,21 @@ func UDPRoutine(name string, decodeFunc decoder.DecoderFunc, workers int, addr s
 
 	if sockReuse {
 		pconn, err := reuseport.ListenPacket("udp", addrUDP.String())
-		defer pconn.Close()
 		if err != nil {
 			return err
 		}
+		defer pconn.Close()
 		var ok bool
 		udpconn, ok = pconn.(*net.UDPConn)
 		if !ok {
 			return err
 		}
 	} else {
 		udpconn, err = net.ListenUDP("udp", &addrUDP)
-		defer udpconn.Close()
 		if err != nil {
 			return err
 		}
+		defer udpconn.Close()
 	}
 
 	payload := make([]byte, 9000)