Fix rare TinyProtocol issues

SpigotCore_Main/src/com/comphenix/tinyprotocol/TinyProtocol.java

@@ -80,7 +80,7 @@ public class TinyProtocol implements Listener {
 	}
 
 	public void addFilter(Class<?> packetType, BiFunction<Player, Object, Object> filter) {
-		packetFilters.computeIfAbsent(packetType, c -> new ArrayList<>(1)).add(filter);
+		packetFilters.computeIfAbsent(packetType, c -> Collections.synchronizedList(new ArrayList<>(1))).add(filter);
 	}
 
 	public void removeFilter(Class<?> packetType, BiFunction<Player, Object, Object> filter) {
@@ -128,6 +128,9 @@ public class TinyProtocol implements Listener {
 				return new SecurityException("Could not find channel for player " + player.getName());
 			}));
 
+			if(!channel.isActive())
+				return;
+
 			synchronized (playerInterceptors) {
 				playerInterceptors.put(player, this);
 			}