NetworkBuffer now has valid parameter

Removed NetworkBuffer variable in NetworkMessage
TcpClient DataAvailable parameter type is now int32
Fixed NetworkMessage::EncododeMessage to put the size in the Buffer's header and to validate and fixed DecodeMessage to check the buffer's valid variable
Fixed some methods in TcpClientWindows

include/NetworkBuffer.hpp

@@ -17,6 +17,8 @@ struct NetworkBuffer
 
 	std::vector<byte> header; // size must always be 8
 	std::vector<byte> body;
+
+	bool valid = false;
 };
 
 #endif