minor change: calc_tight_bounds should be a const method

panda/src/pgraph/nodePath.cxx

@@ -5512,7 +5512,7 @@ write_bounds(ostream &out) const {
 ////////////////////////////////////////////////////////////////////
 bool NodePath::
 calc_tight_bounds(LPoint3f &min_point, LPoint3f &max_point,
-                  Thread *current_thread) {
+                  Thread *current_thread) const {
   min_point.set(0.0f, 0.0f, 0.0f);
   max_point.set(0.0f, 0.0f, 0.0f);
   nassertr_always(!is_empty(), false);

panda/src/pgraph/nodePath.h

@@ -785,7 +785,7 @@ PUBLISHED:
   void force_recompute_bounds();
   void write_bounds(ostream &out) const;
   bool calc_tight_bounds(LPoint3f &min_point, LPoint3f &max_point,
-                         Thread *current_thread = Thread::get_current_thread());
+                         Thread *current_thread = Thread::get_current_thread()) const;
 
   void analyze() const;