filter/Convert: add convert_filter_prepare()

src/filter/plugins/ConvertFilterPlugin.cxx

@@ -132,6 +132,12 @@ const FilterPlugin convert_filter_plugin = {
 	convert_filter_init,
 };
 
+PreparedFilter *
+convert_filter_prepare() noexcept
+{
+	return new PreparedConvertFilter();
+}
+
 Filter *
 convert_filter_new(const AudioFormat in_audio_format,
 		   const AudioFormat out_audio_format)

src/filter/plugins/ConvertFilterPlugin.hxx

@@ -20,9 +20,13 @@
 #ifndef MPD_CONVERT_FILTER_PLUGIN_HXX
 #define MPD_CONVERT_FILTER_PLUGIN_HXX
 
+class PreparedFilter;
 class Filter;
 struct AudioFormat;
 
+PreparedFilter *
+convert_filter_prepare() noexcept;
+
 Filter *
 convert_filter_new(AudioFormat in_audio_format,
 		   AudioFormat out_audio_format);