Fix Stream Management ack listner invocation

aborting to early, because of a 'return' statement, when 'continue'
should be used.

Thanks to Daniele Ricci for reporting this bug.

smack-tcp/src/main/java/org/jivesoftware/smack/tcp/XMPPTCPConnection.java

@@ -1720,7 +1720,7 @@ public class XMPPTCPConnection extends AbstractXMPPConnection {
                         }
                         String id = ackedStanza.getStanzaId();
                         if (StringUtils.isNullOrEmpty(id)) {
-                            return;
+                            continue;
                         }
                         PacketListener listener = stanzaIdAcknowledgedListeners.remove(id);
                         if (listener != null) {