### 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
help_menu->add_icon_shortcut(gui_base->get_theme_icon(SNAME("Godot"), SNAME("EditorIcons")), ED_SHORTCUT_AND_COMMAND("editor/about", TTR("About Godot")), HELP_ABOUT);
	}
	help_menu->add_icon_shortcut(gui_base->get_theme_icon(SNAME("Heart"), SNAME("EditorIcons")), ED_SHORTCUT_AND_COMMAND("editor/support_development", TTR("Support Godot Development")), HELP_SUPPORT_GODOT_DEVELOPMENT);
	
	Control *right_spacer = memnew(Control);
	right_spacer->set_mouse_filter(Control::MOUSE_FILTER_PASS);
	right_spacer->set_h_size_flags(Control::SIZE_EXPAND_FILL);
	title_bar->add_child(right_spacer);
	project_run_bar = memnew(EditorRunBar);
	title_bar->add_child(project_run_bar);
	project_run_bar->connect("play_pressed", callable_mp(this, &EditorNode::_project_run_started));
	project_run_bar->connect("stop_pressed", callable_mp(this, &EditorNode::_project_run_stopped));
	HBoxContainer *right_menu_hb = memnew(HBoxContainer);
	title_bar->add_child(right_menu_hb);
	renderer = memnew(OptionButton);
	renderer->set_visible(true);
	renderer->set_flat(true);
	renderer->set_fit_to_longest_item(false);
	renderer->set_focus_mode(Control::FOCUS_NONE);
	renderer->connect("item_selected", callable_mp(this, &EditorNode::_renderer_selected));
	renderer->add_theme_font_override("font", gui_base->get_theme_font(SNAME("bold"), SNAME("EditorFonts")));
	renderer->add_theme_font_size_override("font_size", gui_base->get_theme_font_size(SNAME("bold_size"), SNAME("EditorFonts")));
	renderer->set_tooltip_text(TTR("Choose a renderer."));
	right_menu_hb->add_child(renderer);
	if (can_expand) {
		
		right_menu_spacer = memnew(Control);
		right_menu_spacer->set_mouse_filter(Control::MOUSE_FILTER_PASS);
		title_bar->add_child(right_menu_spacer);
	}