fix(interceptor): Fixed issue with not unsubscribing

Author: prog110

src/interceptor-service.ts

@@ -84,6 +84,7 @@ export class InterceptorService extends Http {
         () => observer.complete()
       );
       observer.add(() => {
+        subscription.unsubscribe();
         this.interceptors.reverse().forEach((interceptor, index) => {
           if (interceptor.onUnsubscribe !== undefined) {
             interceptor.onUnsubscribe(index, url, options);

src/interceptor.ts

@@ -79,7 +79,9 @@ export interface Interceptor {
   /**
    * Invoked when the user unsubscribes while the request is still being handled
    * Use this method to perform cleanup operations that should be performed when the request is cancelled by user
-   * such as stopping progress bar
+   * such as stopping progress bar.
+   * NOTE: This method would be invoked even if none of the other handler methods are called on the interceptor.
+   * So, always do null checks in this handler
    */
   onUnsubscribe?(interceptorStep: number, url: string | Request, options?: RequestOptionsArgs | InterceptorRequestOptionsArgs): void;