Crash on /stop

[xpyctum]

> java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
        at java.util.HashMap$ValueIterator.next(HashMap.java:1458)
        at cn.nukkit.raknet.server.SessionManager.receiveStream(SessionManager.java:358)
        at cn.nukkit.raknet.server.SessionManager.tickProcessor(SessionManager.java:79)
        at cn.nukkit.raknet.server.SessionManager.run(SessionManager.java:68)
        at cn.nukkit.raknet.server.SessionManager.<init>(SessionManager.java:56)
        at cn.nukkit.raknet.server.RakNetServer.run(RakNetServer.java:100)

[wu-vincent]

Remember to paste the code with the trace, for example:
at cn.nukkit.raknet.server.SessionManager.receiveStream(SessionManager.java:358)
Then paste codes like this:

357: case RakNet.PACKET_SHUTDOWN:
358:       for (Session session : this.sessions.values()) {
                    this.removeSession(session);
           }

[xpyctum]

@MagicDroidX Using latest build.

[wu-vincent]

@xpyctum This is a notice, because it may change very often. :)

[xpyctum]

@MagicDroidX Ok, will know :)