gobj: don't define GeomVertexReader::empty_buffer in opt3 build

panda/src/gobj/geomVertexReader.cxx

@@ -13,9 +13,9 @@
 
 #include "geomVertexReader.h"
 
-#ifndef NDEBUG
-  // This is defined just for the benefit of having something non-NULL to
-  // return from a nassertr() call.
+#ifdef _DEBUG
+// This is defined just for the benefit of having something non-NULL to
+// return from a nassertr() call.
 const unsigned char GeomVertexReader::empty_buffer[100] = { 0 };
 #endif
 

panda/src/gobj/geomVertexReader.h

@@ -155,7 +155,7 @@ private:
   int _start_row;
   bool _force;
 
-#ifndef NDEBUG
+#ifdef _DEBUG
   // This is defined just for the benefit of having something non-NULL to
   // return from a nassertr() call.
   static const unsigned char empty_buffer[100];