### 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
int idx = tool_menu->get_item_count();
	tool_menu->add_item(p_name, TOOLS_CUSTOM);
	tool_menu->set_item_metadata(idx, p_callback);
}
void EditorNode::add_tool_submenu_item(const String &p_name, PopupMenu *p_submenu) {
	ERR_FAIL_NULL(p_submenu);
	ERR_FAIL_COND(p_submenu->get_parent() != nullptr);
	tool_menu->add_child(p_submenu);
	tool_menu->add_submenu_item(p_name, p_submenu->get_name(), TOOLS_CUSTOM);
}
void EditorNode::remove_tool_menu_item(const String &p_name) {
	for (int i = 0; i < tool_menu->get_item_count(); i++) {
		if (tool_menu->get_item_id(i) != TOOLS_CUSTOM) {
			continue;
		}
		if (tool_menu->get_item_text(i) == p_name) {
			if (tool_menu->get_item_submenu(i) != "") {
				Node *n = tool_menu->get_node(tool_menu->get_item_submenu(i));
				tool_menu->remove_child(n);
				memdelete(n);
			}
			tool_menu->remove_item(i);
			tool_menu->reset_size();
			return;
		}
	}
}
PopupMenu *EditorNode::get_export_as_menu() {