### 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_slot[i]->show();
			}
			WindowWrapper *wrapper = Object::cast_to<WindowWrapper>(node);
			if (restore_window_on_load && floating_docks_dump.has(name)) {
				_restore_floating_dock(floating_docks_dump[name], node, i);
			} else if (wrapper) {
				_dock_floating_close_request(wrapper);
			}
		}
		if (!p_layout->has_section_key(p_section, "dock_" + itos(i + 1) + "_selected_tab_idx")) {
			continue;
		}
		int selected_tab_idx = p_layout->get_value(p_section, "dock_" + itos(i + 1) + "_selected_tab_idx");
		if (selected_tab_idx >= 0 && selected_tab_idx < dock_slot[i]->get_tab_count()) {
			dock_slot[i]->call_deferred("set_current_tab", selected_tab_idx);
		}
	}
	for (int i = 0; i < vsplits.size(); i++) {
		if (!p_layout->has_section_key(p_section, "dock_split_" + itos(i + 1))) {
			continue;
		}
		int ofs = p_layout->get_value(p_section, "dock_split_" + itos(i + 1));
		vsplits[i]->set_split_offset(ofs);
	}
	for (int i = 0; i < hsplits.size(); i++) {
		if (!p_layout->has_section_key(p_section, "dock_hsplit_" + itos(i + 1))) {
			continue;
		}
		int ofs = p_layout->get_value(p_section, "dock_hsplit_" + itos(i + 1));
		hsplits[i]->set_split_offset(ofs);