title: React Navigation check if previous screen exists
body: <p>I am looking desperately for a possibility to check if a previous screen exists in ReactNavigation. </p>
  
  <p>Using <code>this.props.navigation.goBack()</code> returns <code>false</code> if no previous route exists, but I can not use it because if a previous route exists I get redirected.  </p>
  
  <p>Is there a possibility to check if I opened the app instead of navigated from another screen to the Home screen? </p>
  
  <p>Thank you. I am not using Redux. It would make such stuff easier but I would like to avoid using it at the moment. </p>