message: docs: fix logging upon search in example tutorial
  When no errors are thrown but empty array is returned we should log different message.
  PR Close
diff: @@ -86,7 +86,9 @@ export class HeroService {
  return of([]);
  }
  return this.http.get<Hero[]>(`${this.heroesUrl}/?name=${term}`).pipe(
  - tap(_ => this.log(`found heroes matching "${term}"`)),
  + tap(x => x.length ?
  + this.log(`found heroes matching "${term}"`) :
  + this.log(`no heroes matching "${term}"`)),
  catchError(this.handleError<Hero[]>('searchHeroes', []))
  );
  }
  