Attach (recommended) or Link to PDF file here: [ACORD 0211 2016-09 Acroform BLANK.pdf](https://github.com/mozilla/pdf.js/files/6353664/ACORD.0211.2016-09.Acroform.BLANK.pdf)

Configuration:
- Web browser and its version: Google Chrome Version 90.0.4430.72 (Official Build) (x86_64)
- Operating system and its version: Windows 10 Pro 20H2
- PDF.js version: 2.7.570
- Is a browser extension: No

Steps to reproduce the problem:
1. Load attached form into PDFViewer
2. Call saveDocument method on loaded document proxy

What is the expected behavior: should not crash

What went wrong? (add screenshot)
It crashes in writer.js. Line 273 as of 21 Apr 2021.
![image](https://user-images.githubusercontent.com/10527821/115615989-4d747900-a2f8-11eb-8e6a-fa3070d813a7.png)

Line that crashes: 
![image](https://user-images.githubusercontent.com/10527821/115616056-6846ed80-a2f8-11eb-8df1-b4633d3e5e8e.png)

Potential fix: 
![image](https://user-images.githubusercontent.com/10527821/115616270-af34e300-a2f8-11eb-82c9-c13bfd111fe4.png)

Potential fix is based on this line if worker.js file: 
![image](https://user-images.githubusercontent.com/10527821/115616437-e0151800-a2f8-11eb-947c-d89e72774bd5.png)


Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension): not hosted

* See the License for the specific language governing permissions and
 * limitations under the License.
 */
import {
  AbortException,
  arrayByteLength,
  arraysToBytes,
  createPromiseCapability,
  getVerbosityLevel,
  info,
  InvalidPDFException,
  isString,
  MissingPDFException,
  PasswordException,
  setVerbosityLevel,
  stringToPDFString,
  UnexpectedResponseException,
  UnknownErrorException,
  UNSUPPORTED_FEATURES,
  VerbosityLevel,
  warn,
} from "../shared/util.js";
import { clearPrimitiveCaches, Dict, Ref } from "./primitives.js";
import { LocalPdfManager, NetworkPdfManager } from "./pdf_manager.js";
import { incrementalUpdate } from "./writer.js";
import { isNodeJS } from "../shared/is_node.js";
import { MessageHandler } from "../shared/message_handler.js";
import { PDFWorkerStream } from "./worker_stream.js";
import { XRefParseException } from "./core_utils.js";
class WorkerTask {