fix(router): throw an error when encounter undefined route (#12389)

modules/@angular/router/src/router_module.ts

@@ -8,7 +8,6 @@
 
 import {APP_BASE_HREF, HashLocationStrategy, Location, LocationStrategy, PathLocationStrategy, PlatformLocation} from '@angular/common';
 import {ANALYZE_FOR_ENTRY_COMPONENTS, APP_BOOTSTRAP_LISTENER, ApplicationRef, Compiler, Inject, Injector, ModuleWithProviders, NgModule, NgModuleFactoryLoader, OpaqueToken, Optional, Provider, SkipSelf, SystemJsNgModuleLoader} from '@angular/core';
-
 import {Route, Routes} from './config';
 import {RouterLink, RouterLinkWithHref} from './directives/router_link';
 import {RouterLinkActive} from './directives/router_link_active';