renderer: copy cache path before render to avoid race conditions

app/render/backend/renderworker.h

@@ -50,11 +50,6 @@ public:
     available_ = a;
   }
 
-  void SetViewerNode(ViewerOutput* viewer)
-  {
-    viewer_ = viewer;
-  }
-
   void SetVideoParams(const VideoParams& params)
   {
     video_params_ = params;
@@ -90,6 +85,11 @@ public:
     generate_audio_previews_ = e;
   }
 
+  void SetCachePath(const QString& s)
+  {
+    cache_path_ = s;
+  }
+
   void Hash(RenderTicketPtr ticket, ViewerOutput* viewer, const QVector<rational>& times);
 
   /**
@@ -186,14 +186,14 @@ private:
 
   bool generate_audio_previews_;
 
-  ViewerOutput* viewer_;
-
   QHash<Node*, Node*>* copy_map_;
 
   RenderMode::Mode render_mode_;
 
   QTimer* cleanup_timer_;
 
+  QString cache_path_;
+
   static const int kMaxDecoderLife;
 
 private slots: