Fix data race with mixer thread performance measurements

src/window.cpp

@@ -3237,6 +3237,9 @@ void UpdateWindows()
 	PerformanceMeasurer framerate(PFE_DRAWING);
 	PerformanceAccumulator::Reset(PFE_DRAWWORLD);
 
+	extern void ProcessPendingPerformanceMeasurements();
+	ProcessPendingPerformanceMeasurements();
+
 	CallWindowRealtimeTickEvent(delta_ms);
 
 	static GUITimer network_message_timer = GUITimer(1);