### 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
current_menu_option = -1;
	if (accept) {
		accept->set_ok_button_text(p_title);
		accept->set_text(p_text);
		EditorInterface::get_singleton()->popup_dialog_centered(accept);
	}
}
void EditorNode::show_save_accept(const String &p_text, const String &p_title) {
	current_menu_option = -1;
	if (save_accept) {
		save_accept->set_ok_button_text(p_title);
		save_accept->set_text(p_text);
		EditorInterface::get_singleton()->popup_dialog_centered(save_accept);
	}
}
void EditorNode::show_warning(const String &p_text, const String &p_title) {
	if (warning) {
		warning->set_text(p_text);
		warning->set_title(p_title);
		EditorInterface::get_singleton()->popup_dialog_centered(warning);
	} else {
		WARN_PRINT(p_title + " " + p_text);
	}
}
void EditorNode::_copy_warning(const String &p_str) {