correct old usage

panda/src/pgraph/light.cxx

@@ -100,7 +100,7 @@ get_vector_to_light(LVector3f &, const LPoint3f &, const LMatrix4f &) {
 ////////////////////////////////////////////////////////////////////
 GeomNode *Light::
 get_viz() {
-  CDReader cdata(_cycler);
+  CDLockedReader cdata(_cycler);
   if (cdata->_viz_geom_stale) {
     CDWriter cdata_w(_cycler, cdata);
 

panda/src/pgraph/light.h

@@ -25,6 +25,7 @@
 #include "luse.h"
 #include "cycleData.h"
 #include "cycleDataReader.h"
+#include "cycleDataLockedReader.h"
 #include "cycleDataWriter.h"
 #include "pipelineCycler.h"
 #include "updateSeq.h"
@@ -118,6 +119,7 @@ private:
 
   PipelineCycler<CData> _cycler;
   typedef CycleDataReader<CData> CDReader;
+  typedef CycleDataLockedReader<CData> CDLockedReader;
   typedef CycleDataWriter<CData> CDWriter;
 
 protected: