tag: new tag "Mood"

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1435

src/db/plugins/ProxyDatabasePlugin.cxx

@@ -201,6 +201,9 @@ static constexpr struct {
 	{ TAG_MOVEMENT, MPD_TAG_MOVEMENT },
 	{ TAG_MOVEMENTNUMBER, MPD_TAG_MOVEMENTNUMBER },
 	{ TAG_LOCATION, MPD_TAG_LOCATION },
+#endif
+#if LIBMPDCLIENT_CHECK_VERSION(2,21,0)
+	{ TAG_MOOD, MPD_TAG_MOOD },
 #endif
 	{ TAG_NUM_OF_ITEM_TYPES, MPD_TAG_COUNT }
 };