test/DumpDecoderClient: allow overriding GetCommand()

test/DumpDecoderClient.cxx

@@ -101,7 +101,7 @@ DumpDecoderClient::SubmitData(gcc_unused InputStream *is,
 	}
 
 	gcc_unused ssize_t nbytes = write(STDOUT_FILENO, data, datalen);
-	return DecoderCommand::NONE;
+	return GetCommand();
 }
 
 DecoderCommand
@@ -113,7 +113,7 @@ DumpDecoderClient::SubmitTag(gcc_unused InputStream *is,
 	for (const auto &i : tag)
 		fprintf(stderr, "  %s=%s\n", tag_item_names[i.type], i.value);
 
-	return DecoderCommand::NONE;
+	return GetCommand();
 }
 
 static void

test/DumpDecoderClient.hxx

@@ -27,7 +27,7 @@
  * A #DecoderClient implementation which dumps metadata to stderr and
  * decoded data to stdout.
  */
-class DumpDecoderClient final : public DecoderClient {
+class DumpDecoderClient : public DecoderClient {
 	bool initialized = false;
 
 	uint16_t prev_kbit_rate = 0;