Fix MUC participantStatusListeners

Thanks to Anno van Vliet for reporting the issue and proposing the fix.

smack-extensions/src/main/java/org/jivesoftware/smackx/muc/MultiUserChat.java

@@ -197,7 +197,7 @@ public class MultiUserChat {
                 case unavailable:
                     occupantsMap.remove(from);
                     MUCUser mucUser = MUCUser.from(packet);
-                    if (mucUser != null && mucUser.getStatus() != null) {
+                    if (mucUser != null && mucUser.hasStatus()) {
                         // Fire events according to the received presence code
                         checkPresenceCode(
                             mucUser.getStatus(),

smack-extensions/src/main/java/org/jivesoftware/smackx/muc/packet/MUCUser.java

@@ -118,6 +118,19 @@ public class MUCUser implements ExtensionElement {
         return statusCodes;
     }
 
+    /**
+     * Returns true if this MUCUser instance has also {@link Status} information.
+     * <p>
+     * If <code>true</code> is returned, then {@link #getStatus()} will return a non-empty set.
+     * </p>
+     *
+     * @return true if this MUCUser has status information.
+     * @since 4.1
+     */
+    public boolean hasStatus() {
+        return !statusCodes.isEmpty();
+    }
+
     /**
      * Returns the notification that the room has been destroyed. After a room has been destroyed,
      * the room occupants will receive a Presence packet of type 'unavailable' with the reason for