Prevent elapsedTime to be negative (#467)

Also fix the `elapsedTime` for Redis.

tap/extensions/kafka/main.go

@@ -149,6 +149,9 @@ func (d dissecting) Analyze(item *api.OutputChannelItem, resolvedSource string,
 
 	request["url"] = summary
 	elapsedTime := item.Pair.Response.CaptureTime.Sub(item.Pair.Request.CaptureTime).Round(time.Millisecond).Milliseconds()
+	if elapsedTime < 0 {
+		elapsedTime = 0
+	}
 	return &api.MizuEntry{
 		Protocol: _protocol,
 		Source: &api.TCP{