Fixed change nickname may cause occupants duplicated issue

User A joined chatroom, then user B joined chatroom. If user A changed his nickname, it may cause duplicated occupants.

This is because the first unavailable presence has 303 status code but no 110 status code, then myRoomJID and myNickname will be update to old JID and nickname. 

Then the second available presence without 110 status code, and can't match wrong JID or nickname (L990 ~ L991). It will be treat as a normal occupant joins chatroom.

Tested on openfire 3.9.3.