Fix class/struct mismatch

gtk2_ardour/loudness_dialog.h

@@ -36,7 +36,7 @@
 #include "loudness_settings.h"
 
 namespace ARDOUR {
-	class TimelineRange;
+	struct TimelineRange;
 	class ExportAnalysis;
 	class ExportStatus;
 	class PluginInsert;

libs/ardour/ardour/utils.h

@@ -54,7 +54,8 @@ class Route;
 class Track;
 class Region;
 class Source;
-class TimelineRange;
+
+struct TimelineRange;
 
 LIBARDOUR_API std::string legalize_for_path (const std::string& str);
 LIBARDOUR_API std::string legalize_for_universal_path (const std::string& str);