docs: fix division by zero in progress events example (#46077)

If the `event.total` is undefined, this line would have generated a `NaN` due to division by zero. I suppose, that a `0` would be more suitable for this case.

PR Close #46077

aio/content/examples/http/src/app/uploader/uploader.service.ts

@@ -62,7 +62,7 @@ export class UploaderService {
 
       case HttpEventType.UploadProgress:
         // Compute and show the % done:
-        const percentDone = Math.round(100 * event.loaded / (event.total ?? 0));
+        const percentDone = event.total ? Math.round(100 * event.loaded / event.total) : 0;
         return `File "${file.name}" is ${percentDone}% uploaded.`;
 
       case HttpEventType.Response: