### 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
if (selected_tab_idx >= 0) {
			p_layout->set_value(p_section, "dock_" + itos(i + 1) + "_selected_tab_idx", selected_tab_idx);
		}
	}
	Dictionary floating_docks_dump;
	for (WindowWrapper *wrapper : floating_docks) {
		Control *dock = wrapper->get_wrapped_control();
		Dictionary dock_dump;
		dock_dump["window_rect"] = wrapper->get_window_rect();
		int screen = wrapper->get_window_screen();
		dock_dump["window_screen"] = wrapper->get_window_screen();
		dock_dump["window_screen_rect"] = DisplayServer::get_singleton()->screen_get_usable_rect(screen);
		String name = dock->get_name();
		floating_docks_dump[name] = dock_dump;
		int dock_slot_id = wrapper->get_meta("dock_slot");
		String config_key = "dock_" + itos(dock_slot_id + 1);
		String names = p_layout->get_value(p_section, config_key, "");
		if (names.is_empty()) {
			names = name;
		} else {
			names += "," + name;
		}
		p_layout->set_value(p_section, config_key, names);
	}
	p_layout->set_value(p_section, "dock_floating", floating_docks_dump);
	for (int i = 0; i < vsplits.size(); i++) {
		if (vsplits[i]->is_visible_in_tree()) {
			p_layout->set_value(p_section, "dock_split_" + itos(i + 1), vsplits[i]->get_split_offset());
		}
	}