### 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
default_layout->set_value(docks_section, "dock_3", "Scene,Import");
	default_layout->set_value(docks_section, "dock_4", "FileSystem");
	default_layout->set_value(docks_section, "dock_5", "Inspector,Node,History");
	for (int i = 0; i < vsplits.size(); i++) {
		default_layout->set_value(docks_section, "dock_split_" + itos(i + 1), 0);
	}
	default_layout->set_value(docks_section, "dock_hsplit_1", 0);
	default_layout->set_value(docks_section, "dock_hsplit_2", 270 * EDSCALE);
	default_layout->set_value(docks_section, "dock_hsplit_3", -270 * EDSCALE);
	default_layout->set_value(docks_section, "dock_hsplit_4", 0);
	_update_layouts_menu();
	
	bottom_panel = memnew(PanelContainer);
	bottom_panel->add_theme_style_override("panel", gui_base->get_theme_stylebox(SNAME("BottomPanel"), SNAME("EditorStyles")));
	center_split->add_child(bottom_panel);
	center_split->set_dragger_visibility(SplitContainer::DRAGGER_HIDDEN);
	bottom_panel_vb = memnew(VBoxContainer);
	bottom_panel->add_child(bottom_panel_vb);
	bottom_panel_hb = memnew(HBoxContainer);
	bottom_panel_hb->set_custom_minimum_size(Size2(0, 24 * EDSCALE)); 
	bottom_panel_vb->add_child(bottom_panel_hb);
	bottom_panel_hb_editors = memnew(HBoxContainer);
	bottom_panel_hb_editors->set_h_size_flags(Control::SIZE_EXPAND_FILL);
	bottom_panel_hb->add_child(bottom_panel_hb_editors);
	editor_toaster = memnew(EditorToaster);
	bottom_panel_hb->add_child(editor_toaster);
	VBoxContainer *version_info_vbc = memnew(VBoxContainer);
	bottom_panel_hb->add_child(version_info_vbc);