fix(http): check whether Zone is defined (#51119)

Accessing the `Zone` variable without checking if it's defined or not
leads to an error "Zone is not defined" if zone.js is not imported (nooped).
This commit adds an additional check before getting the current zone where
the `doRequest` is being called.

PR Close #51119

packages/common/http/src/fetch.ts

@@ -109,7 +109,9 @@ export class FetchBackend implements HttpBackend {
       let decoder: TextDecoder;
       let partialText: string|undefined;
 
-      const reqZone = Zone.current;
+      // We have to check whether the Zone is defined in the global scope because this may be called
+      // when the zone is nooped.
+      const reqZone = typeof Zone !== 'undefined' && Zone.current;
 
       // Perform response processing outside of Angular zone to
       // ensure no excessive change detection runs are executed
@@ -130,12 +132,13 @@ export class FetchBackend implements HttpBackend {
                 (partialText ?? '') + (decoder ??= new TextDecoder).decode(value, {stream: true}) :
                 undefined;
 
-            reqZone.run(() => observer.next({
+            const reportProgress = () => observer.next({
               type: HttpEventType.DownloadProgress,
               total: contentLength ? +contentLength : undefined,
               loaded: receivedLength,
               partialText,
-            } as HttpDownloadProgressEvent));
+            } as HttpDownloadProgressEvent);
+            reqZone ? reqZone.run(reportProgress) : reportProgress();
           }
         }
       });