### 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
_screenshot();
}
void EditorNode::_screenshot(bool p_use_utc) {
	String name = "editor_screenshot_" + Time::get_singleton()->get_datetime_string_from_system(p_use_utc).replace(":", "") + ".png";
	NodePath path = String("user:") + name;
	_save_screenshot(path);
	if (EDITOR_GET("interface/editor/automatically_open_screenshots")) {
		OS::get_singleton()->shell_show_in_file_manager(ProjectSettings::get_singleton()->globalize_path(path), true);
	}
}
void EditorNode::_save_screenshot(NodePath p_path) {
	Control *editor_main_screen = EditorInterface::get_singleton()->get_editor_main_screen();
	ERR_FAIL_COND_MSG(!editor_main_screen, "Cannot get the editor main screen control.");
	Viewport *viewport = editor_main_screen->get_viewport();
	ERR_FAIL_COND_MSG(!viewport, "Cannot get a viewport from the editor main screen.");
	Ref<ViewportTexture> texture = viewport->get_texture();
	ERR_FAIL_COND_MSG(texture.is_null(), "Cannot get a viewport texture from the editor main screen.");
	Ref<Image> img = texture->get_image();
	ERR_FAIL_COND_MSG(img.is_null(), "Cannot get an image from a viewport texture of the editor main screen.");
	Error error = img->save_png(p_path);
	ERR_FAIL_COND_MSG(error != OK, "Cannot save screenshot to file '" + p_path + "'.");
}
void EditorNode::_tool_menu_option(int p_idx) {