title: Returning caught error observable from catchError in HttpInterceptor causes error loop
body: <p>I have a simple interceptor that handles requests and catches any http error using RXJS catchError. The second argument received in catchError is the caught observable. I want to, in some cases, return this error and let it propagate up to the error handler in the subscribe function. The problem is that returning th caught error causes an infinite loop (as seen in the example: <a href="https://stackblitz.com/edit/angular-u4gakr" rel="noreferrer">https://stackblitz.com/edit/angular-u4gakr</a>)</p>
  
  <p>The intercept function in the interceptor where the catchError is stuck in a loop when reciving an HTTP error, like 404:</p>
  
  <pre><code>return next.handle(request)
    .pipe(
      catchError((error, caught$) =&gt; {
        console.log('Returning caught observable'); 
        return caught$;
      })
    );
  </code></pre>
  
  <p>I have probably misunderstood something about the interceptor or RxJS catchError. Any suggestion?</p>