### 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
EditorSettings::get_singleton()->add_property_hint(PropertyInfo(Variant::INT, "interface/inspector/default_color_picker_mode", PROPERTY_HINT_ENUM, "RGB,HSV,RAW,OKHSL", PROPERTY_USAGE_DEFAULT));
	EDITOR_DEF("interface/inspector/default_color_picker_shape", (int32_t)ColorPicker::SHAPE_OKHSL_CIRCLE);
	EditorSettings::get_singleton()->add_property_hint(PropertyInfo(Variant::INT, "interface/inspector/default_color_picker_shape", PROPERTY_HINT_ENUM, "HSV Rectangle,HSV Rectangle Wheel,VHS Circle,OKHSL Circle", PROPERTY_USAGE_DEFAULT));
	ED_SHORTCUT("canvas_item_editor/pan_view", TTR("Pan View"), Key::SPACE);
	const Vector<String> textfile_ext = ((String)(EDITOR_GET("docks/filesystem/textfile_extensions"))).split(",", false);
	for (const String &E : textfile_ext) {
		textfile_extensions.insert(E);
	}
	theme_base = memnew(Control);
	add_child(theme_base);
	theme_base->set_anchors_and_offsets_preset(Control::PRESET_FULL_RECT);
	gui_base = memnew(Panel);
	theme_base->add_child(gui_base);
	gui_base->set_anchors_and_offsets_preset(Control::PRESET_FULL_RECT);
	theme_base->set_theme(theme);
	gui_base->set_theme(theme);
	gui_base->add_theme_style_override("panel", gui_base->get_theme_stylebox(SNAME("Background"), SNAME("EditorStyles")));
	resource_preview = memnew(EditorResourcePreview);
	add_child(resource_preview);
	progress_dialog = memnew(ProgressDialog);
	progress_dialog->set_unparent_when_invisible(true);
	
	gui_base->set_anchor(SIDE_RIGHT, Control::ANCHOR_END);
	gui_base->set_anchor(SIDE_BOTTOM, Control::ANCHOR_END);
	gui_base->set_end(Point2(0, 0));
	main_vbox = memnew(VBoxContainer);
	gui_base->add_child(main_vbox);
	main_vbox->set_anchors_and_offsets_preset(Control::PRESET_FULL_RECT, Control::PRESET_MODE_MINSIZE, gui_base->get_theme_constant(SNAME("window_border_margin"), SNAME("Editor")));
	main_vbox->add_theme_constant_override("separation", gui_base->get_theme_constant(SNAME("top_bar_separation"), SNAME("Editor")));
	title_bar = memnew(EditorTitleBar);