Fix error message being printed when importing an OBJ with no surfaces

An OBJ with no surfaces is valid, and typically happens when
you import an OBJ mesh with no associated MTL file.

editor/import/3d/resource_importer_obj.cpp

@@ -425,9 +425,13 @@ static Error _parse_obj(const String &p_path, List<Ref<ImporterMesh>> &r_meshes,
 				}
 
 				if (!current_material.is_empty()) {
-					mesh->set_surface_name(mesh->get_surface_count() - 1, current_material.get_basename());
+					if (mesh->get_surface_count() >= 1) {
+						mesh->set_surface_name(mesh->get_surface_count() - 1, current_material.get_basename());
+					}
 				} else if (!current_group.is_empty()) {
-					mesh->set_surface_name(mesh->get_surface_count() - 1, current_group);
+					if (mesh->get_surface_count() >= 1) {
+						mesh->set_surface_name(mesh->get_surface_count() - 1, current_group);
+					}
 				}
 				Array array = surf_tool->commit_to_arrays();