Free a sharing object's own layers only when it takes over the shared ones

src/libslic3r/Print.cpp

@@ -2971,11 +2971,6 @@ void Print::auto_assign_extruders(ModelObject* model_object) const
 
 void  PrintObject::set_shared_object(PrintObject *object)
 {
-    // Orca: from now on m_layers / m_support_layers only alias the shared object's layers, so release the
-    // ones this object still owns (it may have sliced itself before it became shareable again).
-    // Both are no-ops once m_shared_object is set, so this cannot free layers owned by another object.
-    clear_support_layers();
-    clear_layers();
     m_shared_object = object;
     BOOST_LOG_TRIVIAL(info) << __FUNCTION__ << boost::format(": this=%1%, found shared object from %2%")%this%m_shared_object;
 }
@@ -2996,6 +2991,15 @@ void  PrintObject::clear_shared_object()
 void  PrintObject::copy_layers_from_shared_object()
 {
     if (m_shared_object) {
+        // Orca: Print::process() calls this once per slice for each sharing object, after clear_shared_object() has
+        // emptied any earlier alias, so the vectors hold only layers this object sliced itself before it started sharing
+        // (or nothing). Free them here, as clear_support_layers() / clear_layers() would; those skip deletion while
+        // m_shared_object is set. The belt-only data they also free is always empty here, because belt printers never
+        // share layers.
+        for (SupportLayer *layer : m_support_layers)
+            delete layer;
+        for (Layer *layer : m_layers)
+            delete layer;
         m_layers.clear();
         m_support_layers.clear();