### 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
String path = p_resource->get_path();
	if (path.is_resource_file() && !FileAccess::exists(path + ".import")) {
		save_resource_in_path(p_resource, p_resource->get_path());
	} else {
		save_resource_as(p_resource);
	}
}
void EditorNode::save_resource_as(const Ref<Resource> &p_resource, const String &p_at_path) {
	{
		String path = p_resource->get_path();
		if (!path.is_resource_file()) {
			int srpos = path.find("::");
			if (srpos != -1) {
				String base = path.substr(0, srpos);
				if (!get_edited_scene() || get_edited_scene()->get_scene_file_path() != base) {
					show_warning(TTR("This resource can't be saved because it does not belong to the edited scene. Make it unique first."));
					return;
				}
			}
		} else {
			if (FileAccess::exists(path + ".import")) {
				show_warning(TTR("This resource can't be saved because it was imported from another file. Make it unique first."));
				return;
			}