Fix async potion effect

src/main/java/fr/xephi/authme/process/join/AsynchronousJoin.java

@@ -189,7 +189,9 @@ public class AsynchronousJoin implements AsynchronousProcess {
             if (service.getProperty(RegistrationSettings.APPLY_BLIND_EFFECT)) {
                 // Allow infinite blindness effect
                 int blindTimeOut = (registrationTimeout <= 0) ? 99999 : registrationTimeout;
+                bukkitService.runTask(() -> {
                     player.addPotionEffect(new PotionEffect(PotionEffectType.BLINDNESS, blindTimeOut, 2));
+                });
             }
             commandManager.runCommandsOnJoin(player);
         });