Fixed a data race in an example

modules/juce_audio_utils/gui/juce_AudioVisualiserComponent.cpp

@@ -55,8 +55,10 @@ struct AudioVisualiserComponent::ChannelInfo
     {
         if (--subSample <= 0)
         {
-            nextSample %= levels.size();
-            levels.getReference (nextSample++) = value;
+            if (++nextSample == levels.size())
+                nextSample = 0;
+
+            levels.getReference (nextSample) = value;
             subSample = owner.getSamplesPerBlock();
             value = Range<float> (newSample, newSample);
         }
@@ -78,7 +80,7 @@ struct AudioVisualiserComponent::ChannelInfo
     AudioVisualiserComponent& owner;
     Array<Range<float>> levels;
     Range<float> value;
-    int nextSample = 0, subSample = 0;
+    std::atomic<int> nextSample { 0 }, subSample { 0 };
 
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (ChannelInfo)
 };