### 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
dock_tab_move_left->set_flat(true);
	if (gui_base->is_layout_rtl()) {
		dock_tab_move_left->set_icon(theme->get_icon(SNAME("Forward"), SNAME("EditorIcons")));
	} else {
		dock_tab_move_left->set_icon(theme->get_icon(SNAME("Back"), SNAME("EditorIcons")));
	}
	dock_tab_move_left->set_focus_mode(Control::FOCUS_NONE);
	dock_tab_move_left->connect("pressed", callable_mp(this, &EditorNode::_dock_move_left));
	dock_hb->add_child(dock_tab_move_left);
	Label *dock_label = memnew(Label);
	dock_label->set_text(TTR("Dock Position"));
	dock_label->set_h_size_flags(Control::SIZE_EXPAND_FILL);
	dock_label->set_horizontal_alignment(HORIZONTAL_ALIGNMENT_CENTER);
	dock_hb->add_child(dock_label);
	dock_tab_move_right = memnew(Button);
	dock_tab_move_right->set_flat(true);
	if (gui_base->is_layout_rtl()) {
		dock_tab_move_right->set_icon(theme->get_icon(SNAME("Back"), SNAME("EditorIcons")));
	} else {
		dock_tab_move_right->set_icon(theme->get_icon(SNAME("Forward"), SNAME("EditorIcons")));
	}
	dock_tab_move_right->set_focus_mode(Control::FOCUS_NONE);
	dock_tab_move_right->connect("pressed", callable_mp(this, &EditorNode::_dock_move_right));
	dock_hb->add_child(dock_tab_move_right);
	dock_vb->add_child(dock_hb);
	dock_select = memnew(Control);
	dock_select->set_custom_minimum_size(Size2(128, 64) * EDSCALE);
	dock_select->connect("gui_input", callable_mp(this, &EditorNode::_dock_select_input));
	dock_select->connect("draw", callable_mp(this, &EditorNode::_dock_select_draw));
	dock_select->connect("mouse_exited", callable_mp(this, &EditorNode::_dock_popup_exit));