Packets can no longer be written to closed channels.

Author: jhg023

src/main/java/simplenet/Client.java

@@ -476,6 +476,11 @@ private void flush(int i) {
             return;
         }
 
+        if (!channel.isOpen()) {
+            outgoingPackets.clear();
+            return;
+        }
+
         ByteBuffer raw = outgoingPackets.poll();
 
         if (raw == null) {