cache: use render job times to synchronize cache

Ensure old inaccurate jobs are never prioritized over current jobs.

app/task/render/render.cpp

@@ -29,6 +29,8 @@ RenderTask::RenderTask(ViewerOutput* viewer, const VideoRenderingParams &vparams
   video_params_(vparams),
   audio_params_(aparams)
 {
+  job_time_ = QDateTime::currentMSecsSinceEpoch();
+
   // FIXME: This makes a full copy of the node graph every time it starts, there must be a better
   //        way.
   backend_.SetViewerNode(viewer_);

app/task/render/render.h

@@ -63,6 +63,11 @@ protected:
 
   void SetAnchorPoint(const rational& r);
 
+  const qint64& job_time() const
+  {
+    return job_time_;
+  }
+
 private:
   ViewerOutput* viewer_;
 
@@ -74,6 +79,8 @@ private:
 
   OpenGLBackend backend_;
 
+  qint64 job_time_;
+
 };
 
 OLIVE_NAMESPACE_EXIT