fps_metrics: fix case where it wouldn't clean up properly

src/fps_metrics.h

@@ -28,10 +28,13 @@ class fpsMetrics {
 
         void calculate(){
             thread_init = true;
-            while (!terminate){
+            while (true){
                 std::unique_lock<std::mutex> lock(mtx);
                 cv.wait(lock, [this] { return run; });
 
+                if (terminate)
+                    break;
+
                 std::vector<float> sorted_values;
                 for (const auto& p : fps_stats)
                     sorted_values.push_back(p.second);