title: XMPP Android - Can't create MultiUserChat
body: <p>I'm using asmack lastest version (now). And I can't create a MultiUserChat on Android.</p>
  
  <p>This is what I get in the log: </p>
  
  <blockquote>
    <p>E/AndroidRuntime(  558): java.lang.ClassCastException:
    org.jivesoftware.smack.packet.DefaultPacketExtension E/AndroidRuntime(
    558):        at
    org.jivesoftware.smackx.muc.MultiUserChat.getMUCUserExtension(MultiUserChat.java:2000)
    E/AndroidRuntime(  558):        at
    org.jivesoftware.smackx.muc.MultiUserChat.create(MultiUserChat.java:364)
    ....</p>
  </blockquote>
  
  <p>Who can help me solve this bug? Thanks!</p>