### 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
} else {
				singleton->main_editor_buttons[i]->disconnect("pressed", callable_mp(singleton, &EditorNode::editor_select));
				singleton->main_editor_buttons[i]->connect("pressed", callable_mp(singleton, &EditorNode::editor_select).bind(i - 1));
			}
		}
		singleton->editor_table.erase(p_editor);
	}
	p_editor->make_visible(false);
	p_editor->clear();
	if (p_config_changed) {
		p_editor->disable_plugin();
	}
	singleton->editor_plugins_over->remove_plugin(p_editor);
	singleton->editor_plugins_force_over->remove_plugin(p_editor);
	singleton->editor_plugins_force_input_forwarding->remove_plugin(p_editor);
	singleton->remove_child(p_editor);
	singleton->editor_data.remove_editor_plugin(p_editor);
	for (KeyValue<ObjectID, HashSet<EditorPlugin *>> &kv : singleton->active_plugins) {
		kv.value.erase(p_editor);
	}
}
void EditorNode::add_extension_editor_plugin(const StringName &p_class_name) {
	ERR_FAIL_COND_MSG(!ClassDB::class_exists(p_class_name), vformat("No such editor plugin registered: %s", p_class_name));
	ERR_FAIL_COND_MSG(!ClassDB::is_parent_class(p_class_name, SNAME("EditorPlugin")), vformat("Class is not an editor plugin: %s", p_class_name));
	ERR_FAIL_COND_MSG(singleton->editor_data.has_extension_editor_plugin(p_class_name), vformat("Editor plugin already added for class: %s", p_class_name));
	EditorPlugin *plugin = Object::cast_to<EditorPlugin>(ClassDB::instantiate(p_class_name));
	singleton->editor_data.add_extension_editor_plugin(p_class_name, plugin);
	add_editor_plugin(plugin);
}
void EditorNode::remove_extension_editor_plugin(const StringName &p_class_name) {