### 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
ResourceImporterScene::add_importer(import_obj2);
			Ref<EditorSceneFormatImporterESCN> import_escn;
			import_escn.instantiate();
			ResourceImporterScene::add_importer(import_escn);
		}
		Ref<ResourceImporterBitMap> import_bitmap;
		import_bitmap.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_bitmap);
	}
	{
		Ref<EditorInspectorDefaultPlugin> eidp;
		eidp.instantiate();
		EditorInspector::add_inspector_plugin(eidp);
		Ref<EditorInspectorRootMotionPlugin> rmp;
		rmp.instantiate();
		EditorInspector::add_inspector_plugin(rmp);
		Ref<EditorInspectorVisualShaderModePlugin> smp;
		smp.instantiate();
		EditorInspector::add_inspector_plugin(smp);
	}
	editor_selection = memnew(EditorSelection);
	EditorFileSystem *efs = memnew(EditorFileSystem);
	add_child(efs);
	
	FileDialog::get_icon_func = _file_dialog_get_icon;
	FileDialog::register_func = _file_dialog_register;
	FileDialog::unregister_func = _file_dialog_unregister;
	EditorFileDialog::get_icon_func = _file_dialog_get_icon;
	EditorFileDialog::register_func = _editor_file_dialog_register;
	EditorFileDialog::unregister_func = _editor_file_dialog_unregister;