### Godot version

v4.2.dev.custom_build [0c2144da9]

### System information

Debian Linux X11 Xfce

### Issue description

Prerequisite: Be in Single Window Mode in the Editor
The Filesystem Dock is unusable when it is floating, which is not expected.
It appears garbled in the top-left corner:
![image](https://github.com/godotengine/godot/assets/6299227/109f7922-97de-44c3-814a-ca7f970e0602)

The following errors are shown:
```
  editor/window_wrapper.cpp:220 - Condition "!is_window_available()" is true.
  editor/window_wrapper.cpp:202 - Condition "!get_window_enabled()" is true. Returning: Rect2i()
  editor/window_wrapper.cpp:207 - Condition "!get_window_enabled()" is true. Returning: -1
  editor/window_wrapper.cpp:207 - Condition "!get_window_enabled()" is true. Returning: -1
```

bisecting lead to #62378
possibly related to #44439

### Steps to reproduce

1. Start a project in the Editor
2. Switch to Single Window Mode in the Editor and reload (if necessary)
3. Make the Filesystem Dock floating

### Minimal reproduction project

Editor issue
if (!is_inside_tree()) {
		defer_load_scene = p_scene;
		return OK;
	}
	if (!p_set_inherited) {
		for (int i = 0; i < editor_data.get_edited_scene_count(); i++) {
			if (editor_data.get_scene_path(i) == p_scene) {
				_scene_tab_changed(i);
				return OK;
			}
		}
		if (!p_force_open_imported && FileAccess::exists(p_scene + ".import")) {
			open_imported->set_text(vformat(TTR("Scene '%s' was automatically imported, so it can't be modified.\nTo make changes to it, a new inherited scene can be created."), p_scene.get_file()));
			open_imported->popup_centered();
			new_inherited_button->grab_focus();
			open_import_request = p_scene;
			return OK;
		}