eth/downloader: fix error aggregator (#27217)

eth/downloader/downloader.go

@@ -663,8 +663,11 @@ func (d *Downloader) spawnSync(fetchers []func() error) error {
 			// it has processed the queue.
 			d.queue.Close()
 		}
-		if err = <-errc; err != nil && err != errCanceled {
-			break
+		if got := <-errc; got != nil {
+			err = got
+			if got != errCanceled {
+				break // receive a meaningful error, bubble it up
+			}
 		}
 	}
 	d.queue.Close()