### 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
Size2 s = dock_select->get_size();
	s.y /= 2.0;
	s.x /= 6.0;
	Color used = Color(0.6, 0.6, 0.6, 0.8);
	Color used_selected = Color(0.8, 0.8, 0.8, 0.8);
	Color tab_selected = theme_base->get_theme_color(SNAME("mono_color"), SNAME("Editor"));
	Color unused = used;
	unused.a = 0.4;
	Color unusable = unused;
	unusable.a = 0.1;
	Rect2 unr(s.x * 2, 0, s.x * 2, s.y * 2);
	unr.position += Vector2(2, 5);
	unr.size -= Vector2(4, 7);
	dock_select->draw_rect(unr, unusable);
	dock_tab_move_left->set_disabled(true);
	dock_tab_move_right->set_disabled(true);
	if (dock_popup_selected_idx != -1 && dock_slot[dock_popup_selected_idx]->get_tab_count()) {
		dock_tab_move_left->set_disabled(dock_slot[dock_popup_selected_idx]->get_current_tab() == 0);
		dock_tab_move_right->set_disabled(dock_slot[dock_popup_selected_idx]->get_current_tab() >= dock_slot[dock_popup_selected_idx]->get_tab_count() - 1);
	}
	for (int i = 0; i < DOCK_SLOT_MAX; i++) {
		Vector2 ofs;
		switch (i) {
			case DOCK_SLOT_LEFT_UL: {
			} break;
			case DOCK_SLOT_LEFT_BL: {