Fixed resource packs/login sequence fail, added basic safety restrictions for packet sending before clients are logged in

close #452

src/pocketmine/network/mcpe/protocol/ClientToServerHandshakePacket.php

@@ -29,6 +29,10 @@ use pocketmine\network\mcpe\NetworkSession;
 class ClientToServerHandshakePacket extends DataPacket{
 	const NETWORK_ID = ProtocolInfo::CLIENT_TO_SERVER_HANDSHAKE_PACKET;
 
+	public function canBeSentBeforeLogin() : bool{
+		return true;
+	}
+
 	public function decode(){
 		//No payload
 	}