fixed conditions evaluations, that always resulted in true (#844)

Signed-off-by: Bogdan Bondar <Bogdan.Bondar@bosch-si.com>

hawkbit-repository/hawkbit-repository-jpa/src/main/java/org/eclipse/hawkbit/repository/jpa/JpaSystemManagement.java

@@ -340,7 +340,7 @@ public class JpaSystemManagement implements CurrentTenantCacheKeyGenerator, Syst
                 }
                 return null;
             }));
-        } while (tenants.hasNext() && (query = tenants.nextPageable()) != null);
+        } while ((query = tenants.nextPageable()) != Pageable.unpaged());
 
     }
 }