only set mRendered to true when a frame was actually rendered

thermion_dart/native/src/rendering/RenderThread.cpp

@@ -115,7 +115,7 @@ void RenderThread::iter()
 {
     if (mRender && !mRendered)
     {
-        mRenderTicker->render(0);
+        if(mRenderTicker->render(0)) {
             mRender = false;
             mRendered = true;
         
@@ -134,6 +134,7 @@ void RenderThread::iter()
                 _accumulatedTime = 0.0f;
             }
         }
+    }
     
     std::unique_lock<std::mutex> taskLock(_taskMutex);