title: Angular route paramMap switchMap stops working after 404
body: <p>In my component's ngOnInit, I am using paramMap as suggested in the <a href="https://angular.io/guide/router" rel="nofollow noreferrer">documentation</a> to re-use a component but switch based on the user id provided in the route:</p>
  
  <pre><code>    this.route.paramMap
          .switchMap((params: ParamMap) =&gt; {
              this.errors = false;
              this.busy = true;
              return this.userService.getUser(params.get('id'));
          })
          .subscribe((user) =&gt; {
              this.busy = false;
              this.errors = false;
              // do something with user object...
            }, (error) =&gt; {
              this.busy = false;
              this.errors = true;
              if (error.status === 404) {
                  this.errorMsg = 'User not found';
              }
          });
  </code></pre>
  
  <p>However as soon as the userService.getUser() method throws a 404 error, .switchMap() stops firing when the route params change, to a new user id for example. I've tried throwing .catch() into both the service as well as the component but it seems to have no effect, and it still stops working after a 404. Am I going about this incorrectly?</p>