Ensure sendServerPacket() works in the channel thread as well.

If we're already in the channel event thread, we won't go through
the ChannelProxy code, so, check scheduledProcessing in the write 
method as well.

ProtocolLib/src/main/java/com/comphenix/protocol/injector/netty/ChannelInjector.java

@@ -300,7 +300,7 @@ class ChannelInjector extends ByteToMessageDecoder implements Injector {
 			NetworkMarker marker = null;
 			
 			// This packet has not been seen by the main thread
-			if (event == null) {
+			if (event == null && scheduleProcessPackets.get()) {
 				Class<?> clazz = packet.getClass();
 				
 				// Schedule the transmission on the main thread instead
@@ -459,9 +459,12 @@ class ChannelInjector extends ByteToMessageDecoder implements Injector {
 	public void sendServerPacket(Object packet, NetworkMarker marker, boolean filtered) {
 		saveMarker(packet, marker);
 		
-		scheduleProcessPackets.set(filtered);
-		invokeSendPacket(packet);
-		scheduleProcessPackets.set(true);
+		try {
+			scheduleProcessPackets.set(filtered);
+			invokeSendPacket(packet);
+		} finally {
+			scheduleProcessPackets.set(true);
+		}
 	}
 	
 	/**

ProtocolLib/src/main/java/com/comphenix/protocol/injector/netty/ClosedInjector.java

@@ -4,8 +4,6 @@ import org.bukkit.entity.Player;
 
 import com.comphenix.protocol.PacketType.Protocol;
 import com.comphenix.protocol.events.NetworkMarker;
-import com.comphenix.protocol.events.PacketEvent;
-
 
 /**
  * Represents a closed injector.