Panku tries to set fields on null values

**Describe the bug** Panku version 1.7.9 (customized to add/remove singleton in `_enable_plugin()` and `_disable_plugin()` instead of `_enter_tree()` and `_exit_tree()`) Running the built game, during load (`template_debug`) the following appears:  For `template_release` game just freezes on load. Disabling Panku helps. **Desktop (please complete the following information):** - OS: Windows 10 - Godot: 4.3 (custom build)