merge: fix(server): invert logic to detect events from bot

The logic to ignore events caused by the bot itself accidentally only
includes events comming from the bot.

Invert the logic, where it would process the event either when no user
is present, or the event was _not_ caused by the bot user.

See merge request !91

server/server.go

@@ -114,8 +114,8 @@ func (l *WebhookEventListener) HookHandler(w http.ResponseWriter, req *http.Requ
 	// Contrary to what the name implies this is actually an event related to a MERGE REQUEST
 	// and not an event that is triggered when a merge request is merged
 	case *gitlab.MergeEvent:
-		if eventContent.User != nil &&
-			eventContent.User.ID == l.config.BotUserID {
+		if eventContent.User == nil ||
+			eventContent.User.ID != l.config.BotUserID {
 			processMergeRequestEvent(
 				eventContent,
 				l.client,