### 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
for (int i = 0; i < hsplits.size(); i++) {
		p_layout->set_value(p_section, "dock_hsplit_" + itos(i + 1), hsplits[i]->get_split_offset());
	}
	
	p_layout->set_value(p_section, "dock_filesystem_split", FileSystemDock::get_singleton()->get_split_offset());
	p_layout->set_value(p_section, "dock_filesystem_display_mode", FileSystemDock::get_singleton()->get_display_mode());
	p_layout->set_value(p_section, "dock_filesystem_file_sort", FileSystemDock::get_singleton()->get_file_sort());
	p_layout->set_value(p_section, "dock_filesystem_file_list_display_mode", FileSystemDock::get_singleton()->get_file_list_display_mode());
	PackedStringArray selected_files = FileSystemDock::get_singleton()->get_selected_paths();
	p_layout->set_value(p_section, "dock_filesystem_selected_paths", selected_files);
	Vector<String> uncollapsed_paths = FileSystemDock::get_singleton()->get_uncollapsed_paths();
	p_layout->set_value(p_section, "dock_filesystem_uncollapsed_paths", uncollapsed_paths);
}
void EditorNode::_save_open_scenes_to_config(Ref<ConfigFile> p_layout) {
	PackedStringArray scenes;
	for (int i = 0; i < editor_data.get_edited_scene_count(); i++) {
		String path = editor_data.get_scene_path(i);
		if (path.is_empty()) {
			continue;
		}
		scenes.push_back(path);
	}
	p_layout->set_value(EDITOR_NODE_CONFIG_SECTION, "open_scenes", scenes);
	String currently_edited_scene_path = editor_data.get_scene_path(editor_data.get_edited_scene());
	
	if (!currently_edited_scene_path.is_empty()) {
		p_layout->set_value(EDITOR_NODE_CONFIG_SECTION, "current_scene", currently_edited_scene_path);
	}
}
void EditorNode::save_editor_layout_delayed() {