Unsubscription error when running any default component test using Steps

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If the Steps component is created, but not initialized, then the unsubscription in the ngDestroy method fails, because the subscription property is not set. This happens for instance in the default tests created by angular-cli which just test if a component can be created. If the component uses Steps, then you get an error in the console log and start to wonder what's happening here.

To replicate the bug, add the following spec to src\app\components\steps\steps.spec.ts in the PrimeNG source code:

    it('should create', () => {
        expect(testComponent).toBeTruthy();
    });

The run the tests with ng tests and look at the output in the console. You will see something like

ERROR: 'Error during cleanup of component', Object{component: TestStpesComponent{activeIndex: 1, __ngContext__: [..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...]}, stacktrace: TypeError: Cannot read property 'unsubscribe' of undefined
TypeError: Cannot read property 'unsubscribe' of undefined
    at Steps.ngOnDestroy (http://localhost:9877/_karma_webpack_/webpack:/src/app/components/steps/steps.ts:92:27)

• Angular version: 12.0.5

• PrimeNG version: 12.0.1

I have revently submitted a very simple fix as PR #9881.