Fix many errors and warnings found out by MinGW

src/Nazara/Network/NetPacket.cpp

@@ -146,7 +146,7 @@ namespace Nz
 		if (!m_buffer)
 			m_buffer = std::make_unique<ByteArray>();
 
-		m_buffer->Resize(static_cast<std::size_t>(cursorPos));
+		m_buffer->Resize(minCapacity);
 
 		m_memoryStream.SetBuffer(m_buffer.get(), openMode);
 		m_memoryStream.SetCursorPos(cursorPos);

src/Nazara/Network/TcpClient.cpp

@@ -385,7 +385,7 @@ namespace Nz
 	* \remark Produces a NazaraError because it is a special stream
 	*/
 
-	bool TcpClient::SetCursorPos(UInt64 offset)
+	bool TcpClient::SetCursorPos(UInt64 /*offset*/)
 	{
 		NazaraError("SetCursorPos() cannot be used on sequential streams");
 		return false;

src/Nazara/Network/Win32/SocketImpl.cpp

@@ -437,6 +437,10 @@ namespace Nz
 
 		return result;
 		#else
+		NazaraUnused(fdarray);
+		NazaraUnused(nfds);
+		NazaraUnused(timeout);
+
 		if (error)
 			*error = SocketError_NotSupported;