Fix error where end_ was called twice

source/RobotAPI/components/ArViz/Coin/Visualizer.cpp

@@ -225,6 +225,7 @@ namespace armarx
                         auto layerIDsBefore = getLayerIDs();
 
                         LayerUpdates pulledUpdates = storage->end_pullUpdatesSince(pullUpdateResult);
+                        pullUpdateResult = nullptr;
                         for (LayerUpdate const& update : pulledUpdates.updates)
                         {
                             apply(update);
@@ -252,6 +253,7 @@ namespace armarx
                 storage = nullptr;
                 updateCounter = 0;
                 state = CoinVisualizerState::STOPPED;
+                pullUpdateResult = nullptr;
                 return;
             }
         }