Re-enable printing by object gcode (#3691)

Re-enable printing by object gcide

src/libslic3r/GCode.cpp

@@ -2546,9 +2546,7 @@ void GCode::_do_export(Print& print, GCodeOutputStream &file, ThumbnailsGenerato
                     // another one, set first layer temperatures. This happens before the Z move
                     // is triggered, so machine has more time to reach such temperatures.
                     this->placeholder_parser().set("current_object_idx", int(finished_objects));
-                    //BBS: remove printing_by_object_gcode
-                    //std::string printing_by_object_gcode = this->placeholder_parser_process("printing_by_object_gcode", print.config().printing_by_object_gcode.value, initial_extruder_id);
-                    std::string printing_by_object_gcode;
+                    std::string printing_by_object_gcode = this->placeholder_parser_process("printing_by_object_gcode", print.config().printing_by_object_gcode.value, initial_extruder_id);
                     // Set first layer bed and extruder temperatures, don't wait for it to reach the temperature.
                     this->_print_first_layer_bed_temperature(file, print, printing_by_object_gcode, initial_extruder_id, false);
                     this->_print_first_layer_extruder_temperatures(file, print, printing_by_object_gcode, initial_extruder_id, false);