NativeHTTPRequest: Fix buffer management for neko

src/lime/_internal/backend/native/NativeHTTPRequest.hx

@@ -393,8 +393,9 @@ class NativeHTTPRequest
 	}
 
 	private function curl_onWrite(curl:CURL, output:Bytes):Int
-	{
-		buffer.add(output);
+	{	
+		buffer.addBytes(output, 0, output.length)
+					
 		return output.length;
 	}