fix(router): unsubscribe preload if the route has been preloaded

packages/router/src/router_preloader.ts

@@ -8,7 +8,7 @@
 
 import {Compiler, Injectable, Injector, NgModuleFactoryLoader, NgModuleRef, OnDestroy} from '@angular/core';
 import {Observable, Subscription, from, of } from 'rxjs';
-import {catchError, concatMap, filter, map, mergeAll, mergeMap} from 'rxjs/operators';
+import {catchError, concatMap, filter, map, mergeAll, mergeMap, takeUntil} from 'rxjs/operators';
 
 import {LoadedRouterConfig, Route, Routes} from './config';
 import {Event, NavigationEnd, RouteConfigLoadEnd, RouteConfigLoadStart} from './events';
@@ -122,12 +122,18 @@ export class RouterPreloader implements OnDestroy {
   }
 
   private preloadConfig(ngModule: NgModuleRef<any>, route: Route): Observable<void> {
+    let preloading = false;
     return this.preloadingStrategy.preload(route, () => {
+      preloading = true;
       const loaded$ = this.loader.load(ngModule.injector, route);
       return loaded$.pipe(mergeMap((config: LoadedRouterConfig) => {
         route._loadedConfig = config;
         return this.processRoutes(config.module, config.routes);
       }));
-    });
+    }).pipe(
+      takeUntil(this.router.events.pipe(filter((e) =>
+        (e instanceof RouteConfigLoadEnd) && !preloading && route === e.route
+      )))
+    );
   }
 }